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Slope Percentage Calculator

Calculate slope in percent online — free, step by step. Grade from rise and run, with the percentage and the angle in degrees.

Quick answer
How do you calculate slope in percent?
Slope in percent is the rise divided by the horizontal run, times 100: rise ÷ run · 100. Example: 3 m of rise over 20 m of run gives 3 ÷ 20 · 100 = 15%. The corresponding angle is arctan(rise ÷ run) ≈ 8.53°.
The tool

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Comma or dot as decimal separator, negative values allowed.
Step-by-step
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HowTo

Slope Percentage Calculator — step-by-step

How do you calculate slope in percent?
  1. 1
    Step 1 of 4

    Determine rise and run

    Measure the rise (height) and the horizontal run in the same unit. Example: 3 m rise, 20 m run.

  2. 2
    Step 2 of 4

    Divide rise by run

    3 ÷ 20 = 0.15.

  3. 3
    Step 3 of 4

    Multiply by 100 for the grade

    0.15 · 100 = 15%.

  4. 4
    Step 4 of 4

    Compute the angle (optional)

    The slope angle is arctan(0.15) ≈ 8.53°. Note: a 100% grade is 45°, not 90°.

Examples

Slope Percentage Calculator — examples

Worked examples with full working
3 m / 20 m
3 ÷ 20 · 100
15% (8.53°)
1 m / 1 m
1 ÷ 1 · 100
100% (45°)
5 m / 100 m
5 ÷ 100 · 100
5% (2.86°)
10 m / 8 m
10 ÷ 8 · 100
125% (51.34°)
2 m / 50 m
2 ÷ 50 · 100
4% (2.29°)
12 m / 100 m
12 ÷ 100 · 100
12% (6.84°)
Theory

What does slope in percent mean?

Slope (grade) in percent tells you how many metres of rise occur per 100 metres of horizontal run. It is rise ÷ run · 100, a direct application of percentage maths to the ratio of vertical to horizontal distance. Important: percent grade and angle are not the same. A 100% grade means rise equals run — an angle of 45°, not 90°. The angle is α = arctan(rise ÷ run). Slope percentages appear on road signs, railways, roofs, ramps (accessibility) and in terrain.

Pitfalls

Common mistakes

Percent confused with degrees

A 15% grade is not 15° but ≈ 8.53°. Convert via arctan first.

Run vs hypotenuse

The grade uses the horizontal run, not the sloped path length.

Reading 100% as vertical

100% is 45°. A vertical wall would have infinite slope.
FAQ

Frequently asked questions

Glossary

Glossary — key terms explained simply

Whole (base)
The reference value that equals 100%.
Part (value)
The amount that belongs to a percentage.
Rate
The percentage (per hundred).
Difference
The result of a subtraction (new − old).
Relative
Expressed against a reference, dimensionless.
Absolute
In the unit of the quantity, without reference.
Factor
Number you multiply by (e.g. 1.25 for +25%).
Percentage point
Absolute difference between two percentages.