Slope / Gradient Calculator

Slope / Gradient Calculator

Calculate and convert slope between percentage, gradient ratio, angle, rise or fall, and reduced levels. Optional distance inputs also produce vertical difference and true slope length.

Sign convention: positive = rise from Point A to Point B; negative = fall.

How to use this calculator

1. Choose an input methodUse measurements, two RLs, percentage, ratio or angle.
2. Enter consistent unitsVertical and horizontal measurements must use the same unit.
3. Review and exportCheck direction, ratio, angle, slope length and report assumptions.

Example: A rise of 1.250 m over 25.000 m horizontal distance equals 5%, 1 in 20 and 2.862405°.

1. Enter slope data

Use a negative value for a fall.

2. Results

Enter the required slope data.

Formulas and interpretation

Slope % = vertical difference ÷ horizontal distance × 100. Angle = atan(vertical difference ÷ horizontal distance). Gradient 1 in X = horizontal distance ÷ absolute vertical difference. True slope length = √(horizontal² + vertical²).

A ratio of 1 in 20 is equivalent to 5%. The ratio alone does not show direction, so this calculator reports Rise or Fall separately.

Frequently asked questions

What is the difference between horizontal and slope distance?

Horizontal distance is the plan distance. Slope distance is the longer distance measured along the inclined surface.

Can I calculate from two reduced levels?

Yes. The calculator uses RL(B) − RL(A) as the signed vertical difference.

What does a negative percentage mean?

It means Point B is lower than Point A in the chosen direction.

How do I convert 1 in 40 to a percentage?

Divide 1 by 40 and multiply by 100, giving 2.5%.

Can I use millimetres or feet?

Yes. Use the same unit for vertical and horizontal distances.

Explore more calculators on the Site Survey tools page.