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Have you ever stepped on the scale, seen a number you didn’t like, and felt discouraged, even after weeks of consistent effort at the gym? Or perhaps you’ve been diligently working out, feeling stronger, yet the scale hasn’t budged? This common frustration reveals a fundamental truth: your weight alone tells only a fraction of your health story. To truly understand your well-being and progress, we must look beyond the scale and explore your body composition, specifically your body fat percentage.
Relying solely on your total body weight can be highly misleading. It doesn’t distinguish between muscle, fat, bone, or water—all of which contribute to that single number. This is precisely why a deeper understanding of your body’s makeup is essential for a more accurate assessment of your health and fitness journey.
The Body Mass Index (BMI) is a widely used screening tool that categorizes individuals based on their weight in relation to their height. While simple to calculate, BMI has significant limitations because it does not differentiate between fat mass and lean muscle mass. For instance, a highly muscular athlete might be classified as “overweight” or “obese” by BMI standards, despite having a very low body fat percentage and excellent health.
This demonstrates how BMI can be misleading. Conversely, an individual with a “normal” BMI could have a high percentage of body fat and low muscle mass. This condition, sometimes referred to as “skinny fat,” carries its own set of health risks. Therefore, BMI alone does not provide a complete picture of an individual’s health status or body composition. Both the Centers for Disease Control and Prevention (CDC) and Harvard Health Publishing emphasize these limitations, urging a more comprehensive approach to health assessment.
Body composition refers to the proportion of fat and fat-free mass (muscle, bone, water) in the body. It serves as a more accurate and comprehensive indicator of health than weight or BMI alone. A healthy body composition, characterized by a lower body fat percentage and adequate muscle mass, is associated with numerous health benefits. These include improved metabolic health, a reduced risk of chronic diseases, and better physical function. Understanding body composition allows for a more nuanced assessment of health and fitness progress, moving beyond the simplistic view offered by a scale. As both the American Council on Exercise (ACE) and the Journal of Clinical Densitometry explain, focusing on body composition provides clearer, more actionable insights into your physical state.
- BMI has limitations as it doesn’t distinguish between fat and muscle, often providing a misleading health picture.
- Body composition offers a more comprehensive view of health than weight alone, focusing on the proportion of fat to lean mass.
- Understanding your body fat percentage is crucial for accurate health and fitness assessment, providing insights beyond what a scale can offer.
When we talk about health and fitness, the term “body fat” often carries a negative connotation. However, fat is an essential component of a healthy body, playing numerous vital roles. The key lies in understanding the right amount and type of fat, which is precisely where body fat percentage becomes an invaluable metric.
Body fat percentage is calculated as the total mass of fat divided by total body mass, then multiplied by 100. It represents the proportion of your body that is composed of fat. This metric offers a more insightful look into health and fitness than just your overall weight, as it directly quantifies the amount of adipose tissue in your body. The American Council on Exercise (ACE) emphasizes that this number is a far better indicator of health and fitness progress than the number on a scale.
| Type of Fat | Description | Typical Percentage (Men/Women) | Key Role |
|---|---|---|---|
| Essential Fat | Minimum amount of fat necessary for basic bodily functions. | Men: 3-5% Women: 10-13% |
Maintains body temperature, absorbs fat-soluble vitamins, protects organs, produces hormones. |
| Storage Fat | Accumulates in adipose tissue (subcutaneous and visceral) as an energy reserve. | Varies (excessive amounts linked to health risks) | Energy reserve, insulation, organ protection. |
- Body fat percentage is the proportion of fat in your total body mass, offering a more insightful health metric than weight.
- Essential fat is vital for bodily functions (temperature, organ protection, hormone production), while storage fat serves as an energy reserve.
- Beyond energy storage, fat plays crucial roles in vitamin absorption, insulation, and hormone regulation.
- Monitoring body fat percentage helps assess health risks (e.g., metabolic diseases), optimize fitness and performance, and track progress more accurately than a simple scale.
Understanding your body fat percentage is a powerful step towards better health. Thankfully, you don’t need expensive lab equipment to get an estimate. The Body Fat Calculator is an accessible and convenient tool that can help you begin your journey of understanding your body composition.
A Body Fat Calculator is a tool designed to estimate an individual’s body fat percentage based on various anthropometric measurements and personal data. Its primary purpose is to provide an accessible and relatively quick assessment of body composition, offering insights beyond what a standard weight scale can provide. These calculators serve as a convenient starting point for individuals interested in understanding their body fat levels and tracking changes over time, as explained by the American Council on Exercise (ACE).
At its core, a Body Fat Calculator takes readily available personal data—such as age, gender, height, weight, and sometimes circumference measurements—and applies a mathematical formula to estimate the proportion of fat in your body. The purpose is not to provide a medical diagnosis but to offer a practical, non-invasive way to gauge your body composition. This estimation helps individuals monitor their health, set realistic fitness goals, and track the effectiveness of their diet and exercise programs, moving beyond the limitations of simply tracking weight.
While the exact mechanisms can vary, most Body Fat Calculators operate on fundamental scientific principles to provide their estimations.
The underlying science of these calculators is based on the principle that different body tissues (fat, muscle, bone) have different densities. For example, fat is less dense than muscle. By measuring body dimensions, these formulas attempt to estimate overall body density, which can then be converted into a body fat percentage using equations like the Siri equation (Body Fat % = (495 / Body Density) – 450) or the Brozek equation.
While these methods provide estimations rather than direct measurements, they offer a practical way to gauge body composition without specialized equipment. The accuracy can vary depending on the formula used and the precision of the measurements taken. The Journal of Sports Sciences and the American College of Sports Medicine (ACSM) are key resources for understanding the scientific basis of these estimations.
- Body Fat Calculators estimate body fat percentage using various anthropometric measurements and personal data.
- Common types include online calculators, smart scales (using BIA), and integrated health apps.
- Calculators rely on established formulas that use inputs like age, gender, height, weight, and circumference measurements to estimate body density.
- The science behind these tools converts estimated body density into a body fat percentage, offering a practical, though estimated, view of body composition.
To get the most reliable estimate from a Body Fat Calculator, precision and consistency are paramount. Following a structured approach to measurement and data input will significantly improve the accuracy of your results and make tracking progress more meaningful.
Circumference measurements are crucial for many body fat calculation formulas. Use a flexible, non-stretchable tape measure. Ensure the tape is snug against the skin but not compressing it. Always take measurements on bare skin. For consistency, measure at the same anatomical landmarks each time:
- Waist: At the narrowest point, usually just above the navel, or at the navel if that’s the widest point. Keep your abdomen relaxed and measure after exhaling.
- Neck: Just below the larynx (Adam’s apple), perpendicular to the neck. Ensure the tape is level all around.
- Hips (for women): At the widest point of the buttocks, with feet together.
- Forearm (sometimes used): At the widest point of the forearm, with the arm extended.
Take each measurement two or three times and use the average to minimize error. The American Council on Exercise (ACE) offers detailed instructions for these measurements.
- Always measure at the same time of day (e.g., morning before food/drink and after using the restroom).
- Use the same tape measure each time to avoid discrepancies between different tools.
- Ensure the tape is level around the body part; looking in a mirror can help.
- Do not suck in your stomach or flex muscles during waist measurement; maintain a relaxed posture.
- Have someone else take the measurements if possible, especially for hard-to-reach areas like the neck, to improve accuracy and consistency.
- Record your measurements immediately to avoid forgetting or mixing up numbers.
Consistent technique is more important than absolute perfection, especially when tracking changes over time. The Mayo Clinic emphasizes the importance of consistent measurement practices.
- Incorrect units: Ensure you’re using the correct units (e.g., inches vs. centimeters, pounds vs. kilograms) as specified by the calculator.
- Typos: Double-check all numerical entries. A single digit error can significantly skew the result.
- Inconsistent measurements: As mentioned, variations in how measurements are taken can lead to inaccurate results. Always follow the same protocol.
- Ignoring instructions: Some calculators have specific instructions for where to measure; follow them precisely.
Avoiding these errors will significantly improve the reliability of your results, as highlighted by research in the Journal of Sports Sciences.
The calculator will provide an estimated body fat percentage. Remember that this is an estimation, not an exact measurement. The output should be viewed as a data point to track trends over time rather than a definitive, unchangeable number. Compare your result to general healthy ranges (discussed in the next section) to get an initial understanding of where you stand. Don’t get fixated on a single number; instead, focus on the direction of change if you are working towards a specific goal. If your body fat measurement is consistently decreasing over weeks or months, that’s a positive sign, regardless of minor daily fluctuations. The American Council on Exercise (ACE) advises focusing on trends rather than isolated readings.
- Choose calculators from reliable sources and understand their methodologies for a more accurate body fat measurement.
- Ensure accurate and consistent height, weight, and circumference measurements, taking them at the same time of day.
- Avoid common input errors like incorrect units or typos, and always follow calculator-specific instructions.
- Interpret results as estimations and focus on trends over time rather than fixating on a single number.
Once you have an estimated body fat percentage, the next crucial step is to understand what those numbers signify for your health and fitness. Context is everything, as an “ideal” range can vary significantly based on individual factors.
| Category | Men (Body Fat %) | Women (Body Fat %) | Description |
|---|---|---|---|
| Essential Fat | 2-5% | 10-13% | Minimum fat required for basic physiological function. |
| Athletes | 6-13% | 14-20% | Lower ranges often seen in competitive athletes for performance. |
| Fitness | 14-17% | 21-24% | Lean and fit individuals. |
| Acceptable/Healthy | 18-24% | 25-31% | General healthy range for the population. |
| Obese | 25%+ | 32%+ | Ranges associated with increased health risks. |
Athletes often maintain lower body fat percentages than the general population due to the rigorous demands of their sport, which often require a higher power-to-weight ratio or specific aesthetic criteria. For competitive athletes, especially those in endurance, strength, or aesthetic sports, ranges can be:
These lower ranges are typically achieved through intense training and strict dietary regimens and may not be sustainable or healthy for the average individual. It’s important to note that even within athletes, the “ideal” range can vary based on the specific sport and individual physiology. The American College of Sports Medicine (ACSM) provides guidelines for athletic body composition, emphasizing that these are specialized ranges.
Body fat percentage tends to increase with age, even if weight remains stable. This is often due to a natural decline in muscle mass (sarcopenia) and changes in metabolism. For example, a healthy body fat range for a 20-year-old might differ from that of a 60-year-old. While the general healthy ranges provide a good guideline, it’s important to consider age as a factor and consult with health professionals for personalized advice. The increase in body fat with age is a normal physiological process, but excessive accumulation can still pose health risks. Research in the Journal of Clinical Endocrinology & Metabolism discusses these age-related changes.
When determining your ideal body fat range, it’s crucial to prioritize health over purely aesthetic goals. While a very low body fat percentage might be aesthetically appealing to some, it can be detrimental to health, leading to hormonal imbalances, weakened immune function, nutrient deficiencies, and impaired physical performance. The “sweet spot” is typically within the healthy general population ranges, where the body functions optimally and the risk of chronic diseases is minimized. The World Health Organization (WHO) consistently advocates for health-first approaches. Aesthetic goals should always be pursued within the confines of maintaining good health and sustainable practices.
For personalized guidance on your ideal body fat range, it is highly recommended to consult with health professionals such as a doctor, a registered dietitian, or a certified personal trainer. They can take into account your individual health history, current fitness level, lifestyle, and specific goals to provide tailored recommendations. They can also help you understand the nuances of your body fat measurement and guide you toward sustainable and healthy practices. Organizations like the Academy of Nutrition and Dietetics emphasize the value of professional, individualized advice.
- Healthy body fat percentage ranges differ for men (10-22%) and women (20-32%) due to physiological differences.
- Athletes often have lower body fat, but these ranges may not be healthy or sustainable for the general population.
- Body fat percentage naturally tends to increase with age, a normal physiological process.
- Prioritize health over aesthetics when setting body fat percentage goals, and always consult health professionals for personalized advice on your ideal body fat range.
While a Body Fat Calculator is a convenient and accessible tool for estimating body fat percentage, it’s important to understand its limitations. No estimation method is perfectly accurate, and various factors can influence results. Fortunately, more advanced—albeit less accessible—methods also exist for a precise body fat measurement.
It’s important to recognize that Body Fat Calculators provide estimations, not precise measurements. The results can vary significantly between different online calculators or smart scales, even when using the same input data. This variability stems from the different formulas and algorithms each calculator employs, as well as the inherent limitations of anthropometric or bioelectrical impedance methods. For example, a study in the Journal of Sports Sciences highlighted the discrepancies between various body composition assessment methods. Therefore, it’s best to use one consistent method for tracking progress rather than comparing results across different calculators. Consistency with one tool is more valuable than seeking a single, definitive number from multiple sources.
| Method | Description | Pros | Cons | Accessibility |
|---|---|---|---|---|
| Skinfold Calipers | Measures subcutaneous fat thickness at various sites. | Inexpensive, portable, accurate with skilled user. | Requires training, user-dependent accuracy, measures only subcutaneous fat. | High (calipers are cheap) |
| Bioelectrical Impedance Analysis (BIA) | Sends low electrical current through body to measure resistance. | Convenient, non-invasive, relatively inexpensive for home use. | Highly sensitive to hydration, food intake, temperature; lower accuracy for extremes. | High (smart scales, handheld devices) |
| DEXA Scans | Uses two X-ray beams to measure bone mineral density, fat, and lean mass. | “Gold standard” for accuracy, detailed regional data, excellent for tracking. | Expensive, specialized equipment, small radiation exposure, less accessible. | Low (clinic-based) |
| Hydrostatic Weighing | Measures body density by submerging individual in water. | Historically very accurate, good reference method. | Impractical, requires specialized equipment/personnel, uncomfortable for some. | Very Low (specialized facilities) |
- Body Fat Calculators are estimations and can vary due to different formulas and influencing factors like hydration, food intake, and time of day.
- Skinfold calipers are inexpensive but require significant skill and training for accurate body fat measurement.
- BIA (smart scales) is convenient for home use but highly sensitive to hydration levels, impacting accuracy.
- DEXA scans are the gold standard for accuracy and detailed body composition analysis but are expensive and less accessible.
- Hydrostatic weighing is accurate but highly impractical for general use due to specialized equipment and procedure requirements.
Understanding your body fat percentage is a powerful first step, but the real transformation happens when you translate those numbers into actionable strategies. Improving your body composition—reducing fat and increasing muscle—involves a holistic approach encompassing nutrition, exercise, and lifestyle factors.
To achieve fat loss, a consistent caloric deficit is essential, meaning you consume fewer calories than your body expends. This forces your body to tap into stored fat for energy. For muscle gain, a slight caloric surplus is typically required to fuel muscle protein synthesis and recovery. The specific deficit or surplus depends on individual goals, activity level, and metabolism. A moderate deficit of 300-500 calories per day is often recommended for sustainable fat loss, while a surplus of 250-500 calories can support muscle growth with minimal fat gain. These principles are well-established in sports nutrition, as discussed in the Journal of the International Society of Sports Nutrition (ISSN).
- Protein: Adequate protein intake (e.g., 1.6-2.2 grams per kilogram of body weight) is vital for preserving muscle mass during a caloric deficit and supporting muscle growth during a surplus. Protein also increases satiety, helping to manage hunger.
- Carbohydrates: Provide energy for workouts and daily activities. Prioritize complex carbohydrates (whole grains, fruits, vegetables) for sustained energy, fiber, and essential micronutrients.
- Fats: Essential for hormone production, nutrient absorption (especially fat-soluble vitamins), and overall cellular health. Focus on healthy fats (avocado, nuts, seeds, olive oil) and ensure they comprise 20-35% of your total caloric intake.
The Journal of the International Society of Sports Nutrition (ISSN) provides detailed recommendations for macronutrient distribution.
Prioritizing whole, unprocessed foods is fundamental for a healthier body composition. These foods are typically nutrient-dense, higher in fiber, and lower in added sugars, unhealthy fats, and sodium compared to processed foods. Emphasize lean proteins, a wide variety of fruits and vegetables, whole grains, and healthy fats. This approach supports satiety, provides essential micronutrients, helps regulate blood sugar, and reduces inflammation, all contributing to better body composition outcomes and overall health. The Dietary Guidelines for Americans consistently advocate for a whole-foods-based diet.
Strength training is paramount for improving body composition. It builds and preserves muscle mass, which is metabolically active tissue, meaning it burns more calories at rest than fat tissue. Increased muscle mass can boost your resting metabolic rate, aiding in fat loss even when you’re not exercising. Furthermore, strength training improves bone density, functional strength, and overall physical performance, making everyday tasks easier and reducing injury risk. Aim for 2-4 strength training sessions per week, targeting all major muscle groups, as recommended by the American College of Sports Medicine (ACSM) and the National Strength and Conditioning Association (NSCA).
Cardiovascular exercise (cardio) complements strength training by improving heart health, increasing caloric expenditure, and enhancing endurance. While not as effective as strength training for building muscle, cardio contributes significantly to creating a caloric deficit necessary for fat loss. Incorporate a mix of moderate-intensity steady-state cardio (e.g., brisk walking, jogging) and high-intensity interval training (HIIT) for varied benefits. HIIT can be particularly effective for fat burning and improving cardiovascular fitness in shorter durations. Aim for at least 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity cardio per week, as advised by the American Heart Association.
Regardless of the specific exercises, consistency is the most crucial factor for long-term success in improving body composition. Regular adherence to your exercise regimen yields cumulative benefits. Additionally, progressive overload—gradually increasing the intensity, duration, or resistance of your workouts—is essential to continually challenge your muscles and prevent plateaus. This could mean lifting heavier weights, doing more repetitions, increasing the duration of your cardio, or reducing rest times. Without progressive overload, your body adapts, and progress stalls. The American College of Sports Medicine (ACSM) emphasizes both consistency and progression as fundamental principles of effective training.
Adequate and quality sleep is a powerful, yet often overlooked, component of healthy body composition. Chronic sleep deprivation can disrupt hormones that regulate appetite (ghrelin, which stimulates hunger, and leptin, which signals satiety), leading to increased hunger and cravings for high-calorie, unhealthy foods. It also elevates cortisol levels, a stress hormone that can promote abdominal fat storage and muscle breakdown. Aim for 7-9 hours of quality sleep per night to support metabolic health, muscle recovery, and hormonal balance. The Sleep Foundation provides extensive resources on the importance of sleep.
Chronic stress can significantly impact body composition. When stressed, the body releases cortisol, a hormone that, in excess, can lead to increased appetite, cravings for comfort foods, and a tendency to store fat, particularly in the abdominal area (visceral fat). Chronic stress also impairs recovery from exercise and can hinder muscle growth. Implementing stress management techniques such as mindfulness, meditation, yoga, spending time in nature, or engaging in hobbies can help regulate cortisol levels and support healthier body composition goals. The American Psychological Association details the physiological effects of stress on the body.
Staying well-hydrated is fundamental for overall health and plays a crucial, though often underestimated, role in body composition. Water is essential for countless metabolic processes, nutrient transport to cells, and waste elimination from the body. Drinking enough water can also aid in satiety, potentially reducing overall caloric intake and preventing overeating. Furthermore, proper hydration is vital for optimal physical performance during exercise. Aim to drink plenty of water throughout the day, adjusting intake based on activity level, climate, and individual needs. The Centers for Disease Control and Prevention (CDC) emphasizes the importance of adequate hydration for health.
- Achieve fat loss with a consistent caloric deficit and support muscle gain with a slight caloric surplus.
- Prioritize adequate protein intake, balance macronutrients (carbs, fats), and emphasize whole, unprocessed foods.
- Incorporate both strength training (2-4 times/week) for muscle building and cardiovascular exercise (150 mins moderate/75 mins vigorous per week) for heart health and fat loss.
- Ensure consistency and progressive overload in your exercise regimen to continually challenge your body.
- Prioritize 7-9 hours of quality sleep, actively manage stress, and stay well-hydrated to support optimal body composition.
Stepping beyond the simple number on the scale and embracing a deeper understanding of your body composition is a pivotal moment in your health and fitness journey. By focusing on your body fat percentage, you gain invaluable insights that empower you to make more informed, effective, and sustainable choices for your well-being.
Understanding and monitoring your body fat percentage offers a profound advantage over simply tracking weight. It provides a more accurate and comprehensive picture of your health, revealing the true composition of your body. By focusing on body composition, you gain insights into your metabolic health, identify risks for chronic diseases, and effectively track progress towards fitness and performance goals. This knowledge empowers you to make targeted and effective decisions for your well-being, moving beyond superficial metrics to truly understand what’s happening inside your body.
Body Fat Calculators, whether online, smart scales, or apps, are valuable tools for estimating body fat percentage. They offer an accessible and convenient way to gain initial insights and monitor trends over time, helping you to calculate body fat in a practical manner. However, it’s crucial to remember that they provide estimations and are subject to inaccuracies and variability due to different formulas and influencing factors like hydration. They should be used as one piece of a larger health puzzle, not as the sole determinant of your health status. Combining calculator results with other health markers, such as energy levels, strength, endurance, and overall well-being, provides a more holistic view.
- Consistent Tracking: Regularly use your chosen Body Fat Calculator or method under consistent conditions (e.g., same time of day, same hydration status) to track trends in your body fat percentage. Focus on the direction of change rather than minor fluctuations.
- Holistic Approach: Integrate nutrition strategies (caloric balance, macronutrient optimization, whole foods), a balanced exercise regimen (strength and cardio), and positive lifestyle factors (7-9 hours of quality sleep, effective stress management, and consistent hydration).
- Professional Guidance: Consult with healthcare professionals, registered dietitians, or certified personal trainers for personalized advice and to interpret your results in the context of your unique health history, current fitness level, and specific goals. They can help you refine your strategies and ensure they are safe and effective.
- Focus on Well-being: Remember that true health extends beyond numbers. Prioritize how you feel, your energy levels, your strength, and your overall quality of life. The numbers are a guide, but your well-being is the ultimate measure of success.
- Body fat percentage offers a more accurate and comprehensive health picture than weight alone, providing insights into metabolic health and chronic disease risk.
- Body Fat Calculators are useful estimation tools for monitoring trends in body fat percentage but have inherent limitations and should not be the only answer.
- Use calculators as part of a holistic health assessment, combining them with other health markers and professional guidance.
- Continue your health journey with consistent tracking, a holistic approach to nutrition and exercise, and by prioritizing lifestyle factors like sleep, stress management, and hydration.
Your total body weight and BMI are limited because they don’t distinguish between muscle, fat, bone, or water. BMI, for instance, can misclassify muscular athletes as “overweight” or “obese,” or overlook “skinny fat” individuals with high body fat but normal weight. Body fat percentage, however, directly quantifies the proportion of fat in your body, offering a far more accurate and comprehensive indicator of your health and fitness progress, reflecting your true body composition.
Body fat percentage is the proportion of your total body mass that is composed of fat. It’s a key metric for understanding body composition. There are two main types: Essential fat is the minimum amount necessary for basic bodily functions, like maintaining body temperature, absorbing vitamins, protecting organs, and producing hormones (typically 3-5% for men, 10-13% for women). Storage fat accumulates in adipose tissue as an energy reserve, also providing insulation and organ protection.
Body Fat Calculators estimate your body fat percentage by applying mathematical formulas to various personal data and anthropometric measurements. They work on the principle that different body tissues have different densities. You typically need to input your age, gender, height, weight, and specific circumference measurements such as your waist, neck, and sometimes hips (for women). These inputs allow the calculator to estimate your body density, which is then converted into a body fat percentage.
Healthy body fat percentage ranges vary significantly based on gender and age. For general healthy adults, acceptable ranges are typically 18-24% for men and 25-31% for women. Athletes often have lower percentages (e.g., 6-13% for men, 14-20% for women) due to performance demands. Additionally, body fat percentage naturally tends to increase with age, even if weight remains stable, due to natural declines in muscle mass and changes in metabolism. It’s crucial to consider these factors and prioritize health over purely aesthetic goals.
Body Fat Calculators provide estimations, not perfectly precise measurements, and their accuracy can vary significantly between different tools due to varying formulas and algorithms. Their results can also be influenced by factors like hydration levels, recent food intake, exercise, and time of day. While convenient, they are less accurate than “gold standard” methods like DEXA scans, which offer highly detailed and precise body composition analysis but are expensive and less accessible. Other methods include skinfold calipers (requiring skill) and Bioelectrical Impedance Analysis (BIA) devices (like smart scales), which are convenient but highly sensitive to hydration.
Formula: Mifflin-St Jeor | Source: National Institutes of Health (NIH) — nih.gov
Estimate your body fat percentage using the U.S. Navy method with circumference measurements.
| Description | Men (% Body Fat) |
|---|---|
| Essential Fat | 2 – 5% |
| Athletes | 6 – 13% |
| Fitness | 14 – 17% |
| Average | 18 – 24% |
| Obese | 25% + |
This calculator uses the U.S. Navy Method (also known as the Hodgdon and Beckett formula), which uses circumference measurements to estimate body fat percentage.
Source: U.S. Navy Method (Hodgdon & Beckett, 1984)