Slope calculator
Slope is rise divided by run. Enter a rise and run, a percent, an angle, or a ratio, and see the same slope in every form: percent grade, degrees, 1 in N, inches per foot, and roof pitch.
Last updated: · Free tool by InsightSpatial
Private by design. This tool runs entirely in your browser. What you enter stays on your device. It is not uploaded to us or stored.
Formulas
- Percent grade = rise ÷ run × 100
- Angle = arctangent(rise ÷ run)
- 1 in N: N = run ÷ rise
- Inches per foot and roof pitch (inches per 12 inches) = 12 × rise ÷ run
- Slope length = √(rise² + run²)
Run is the horizontal distance, not the length along the slope. On a map or plan, the horizontal distance is what you measure.
Common slopes
| Use | Written as | Percent | Degrees |
|---|---|---|---|
| Cross slope of a walkway or accessible route (ADA maximum) | 1:48 | 2.08% | 1.2° |
| Pipe drains 3 to 6 inches (IPC minimum) | 1/8 in per ft | 1.04% | 0.6° |
| Pipe drains 2½ inches and smaller (IPC minimum) | 1/4 in per ft | 2.08% | 1.2° |
| Ground falling away from a house: 6 in in the first 10 ft (IRC minimum) | 6 in in 10 ft | 5% | 2.9° |
| Walking surface that is not a ramp (ADA maximum running slope) | 1:20 | 5% | 2.9° |
| Wheelchair ramp (ADA maximum) | 1:12 | 8.33% | 4.8° |
| Roof pitch 4 in 12 | 4:12 | 33.33% | 18.4° |
| Roof pitch 12 in 12 | 12:12 | 100% | 45° |
ADA: 2010 ADA Standards for Accessible Design. IRC: International Residential Code R401.3. IPC: International Plumbing Code 704.1. Local codes may differ; check with your building department.
Questions
How do I calculate percent slope?
Divide the rise by the run and multiply by 100. A drop of 1 foot over 20 feet is 1 ÷ 20 × 100 = 5%. Use the same unit for both.
How do I convert percent grade to degrees?
Degrees = arctangent(percent ÷ 100). A 100% grade is 45°, a 10% grade is about 5.7°, and a 5% grade is about 2.9°.
What is a 2% slope in inches per foot?
About 0.24 inches per foot, close to 1/4 inch per foot. Multiply the percent by 0.12 to get inches per foot.
What is the maximum slope for a wheelchair ramp?
Under the 2010 ADA Standards, 1:12, which is 8.33% or about 4.8°: one inch of rise for every 12 inches of run. Walking surfaces steeper than 1:20 (5%) count as ramps.
What does a roof pitch of 6/12 mean?
The roof rises 6 inches for every 12 inches of horizontal run: a 50% slope, about 26.6°.