Percent grade is rise over horizontal run
Grade compares vertical change with horizontal distance. A 5% grade means 5 units of rise per 100 units of horizontal run; it does not mean 5 degrees. Angle mode converts the same measured ratio using the arctangent.
Measure and calculate
- Measure vertical rise and horizontal run in the same length unit.
- Use a signed rise to distinguish an uphill or downhill direction.
- Choose percent grade or angle, keeping the same observation direction.
Percent grade = 100 × rise ÷ horizontal run.
A worked example
- Inputs
- The measured surface rises 1 ft across a 20 ft horizontal run.
- Calculation
100 × 1 ÷ 20 = 5%. The corresponding angle is arctan(1 ÷ 20), about 2.86°.- Result
- 5 %
The result describes a measured slope. It does not recommend a drainage grade or determine whether the surface is suitable for a particular use.
Read the result
| Output or check | What it means for your project |
|---|---|
| Percent grade | A grade of 5% means 5 units of vertical change per 100 units of horizontal run. It does not mean a 5° angle. |
| Sign and angle | The sign follows your chosen observation direction. Angle mode converts the same rise-to-run ratio; it does not prescribe a drainage slope. |
Common questions
Can I use the sloped surface length as the run?
This model needs horizontal run. Surface length is the sloping side and produces a different ratio.
Is 100% grade vertical?
No. Equal rise and horizontal run give 100%, corresponding to 45°. Vertical geometry has zero horizontal run and is outside this division model.