Slope Percentage Calculator to convert rise and run into percent grade. Enter values, see the formula, and check results with a quick example.
Calculate slope percentage, angle, rise, or run for construction, landscaping, or accessibility projects.
Formulas from standard trigonometry. Source: Omni Calculator — omnicalculator.com
Slope Percentage Calculator Welcome to the Slope Percentage Calculator. If you need to write a slope as a percent for homework, a ramp, or a road sign, you’re in the right place. This guide explains:…
Welcome to the Slope Percentage Calculator. If you need to write a slope as a percent for homework, a ramp, or a road sign, you’re in the right place. This guide explains:
Slope percentage (often called percent grade) shows how much something rises or falls compared to how far it goes forward.
To calculate it by hand, follow these steps:
The formula looks like this: slope percentage = (rise / run) × 100
Sometimes slope is given as an angle (in degrees), and other times it’s given as a percent. They describe the same tilt, just in different ways.
Use tangent (tan):
slope percentage = tan(d) × 100
Here, d is the angle in degrees. If your angle is in radians, convert it to degrees first.
Use inverse tangent (atan):
angle = atan(s/100)
In this formula, s is the slope percentage, and the angle result is in degrees.
The Slope Percentage Calculator is designed to be quick and flexible. You can enter:
It also works the other way around. If you enter a slope percentage, it will calculate the angle in degrees. If you provide only one of the two values (rise or run), the calculator can fill in the missing one once enough information is available.
Important: Keep the angle between -90° and 90°, but not equal to either endpoint. As the angle gets close to ±90°, the slope percentage grows without limit.
Formulas from standard trigonometry. Source: Omni Calculator — omnicalculator.com
Slope percentage (also called grade) tells you how steep something is compared to the horizontal distance. It’s calculated as rise ÷ run × 100.
A 10% slope means it rises 10 units for every 100 units of horizontal run (for example, 10 feet up over 100 feet across).
Keep the units the same for both. If your rise is in inches and your run is in feet, convert one so they match before you calculate.
Use this formula: slope % = (rise / run) × 100
Example:
That’s a 33.3% slope.
Yes. Downhill slopes use a negative rise.
Example:
A negative sign just tells you the direction is down.
They describe the same steepness, just in different formats.
Quick checks that help:
tan(degrees) × 100atan(percent/100)Most calculators can switch between these for you.
A ratio like 1:12 means 1 unit of rise for every 12 units of run.
Convert it like this: (1 ÷ 12) × 100 = 8.33%
Here are a few common ones:
| Ratio (Rise:Run) | Percent |
|---|---|
| 1:12 | 8.33% |
| 1:20 | 5% |
| 1:48 | 2.08% |
Yes. Slope percent is commonly used for roofs, patios, and drainage planning.
A simple reference point people use is 1/4 inch per foot, which is about 2% slope, often used as a minimum target for drainage in many everyday building scenarios. Your local code, material type, and project details still matter, so it’s smart to confirm requirements before building.
This usually happens when the run is very small (or entered as zero). Since slope percent is rise ÷ run × 100, dividing by a tiny number makes the result explode upward.
If you’re measuring something close to vertical, percent slope can become extremely large. In those cases, degrees may feel more intuitive.
Mixing units, or measuring the wrong “run.”
A quick checklist:
The math is exact, but your result is only as good as your measurements.
For better real-world accuracy: