Slope Calculator
Your estimate
- Angle
- 4.76°
- Ratio
- 1 : 12
- Pitch
- 1/121:12
- Slope length
- 12 ft 1/2 in12.04 ft · 3.67 m
- Fall per foot / per metre
- 1 in1 in · 2.5 cm
For ramps, drains, driveways, roofs and maths homework — rise/run, two points, an angle or a percentage.
Updated 2026-10-20 · Based on: roof-pitch geometry and 3 shingle bundles per square.
How to use the Slope Calculator
- Choose how you know the slope: rise and run, two points, an angle or a percent grade.
- Type the numbers.
- Read the slope as a percent, angle, ratio (1 : x), roof pitch and fall per foot.
Formula
Slope = rise ÷ run. Percent grade = rise ÷ run × 100. Angle = arctan(rise ÷ run).
Through two points: m = (y₂ − y₁) ÷ (x₂ − x₁), and the line is y = m x + b with b = y₁ − m x₁.
Worked example
With the values preset in the calculator above: (Rise & run)
- Riser height
- 1 ft
- Tread depth
- 12 ft
- Slope
- 8.33%
- Angle
- 4.76°
- Ratio
- 1 : 12
- Pitch
- 1/12 (1:12)
- Slope length
- 12 ft 1/2 in (12.04 ft)
How to calculate slope
Measure how much the surface rises (or falls) over a horizontal distance, in the same unit. 1 ft of rise over 12 ft of run is 8.33%, an angle of 4.76° — the maximum slope for a wheelchair ramp (1 : 12).
Common slopes
- Drain pipes: ¼ in per foot (2 %) for 3 in pipe and smaller, ⅛ in per foot (1 %) for larger pipe.
- Patios and decks: ⅛–¼ in per foot away from the house.
- Wheelchair ramps (ADA): 1 : 12 (8.33 %) maximum.
- Driveways: up to about 12–15 %.
- Lawn grading: 2 % away from the foundation for the first 10 ft.
Slope percent to degrees
| Slope (%) | Angle | Ratio |
|---|---|---|
| 1 | 0.57° | 1 : 100 |
| 2 | 1.15° | 1 : 50 |
| 5 | 2.86° | 1 : 20 |
| 8.33 | 4.76° | 1 : 12 |
| 10 | 5.71° | 1 : 10 |
| 25 | 14.04° | 1 : 4 |
| 50 | 26.57° | 1 : 2 |
| 100 | 45° | 1 : 1 |
Related guides
Frequently asked questions
How do I convert slope percent to degrees?
Degrees = arctan(percent ÷ 100). A 10 % slope is 5.71°; 100 % is 45°.
What is a 2 % slope in inches per foot?
About ¼ in per foot: 1/4 in.
What is the slope between (1, 2) and (5, 10)?
m = (10 − 2) ÷ (5 − 1) = 2, and the line is y = 2x + 0.
Is slope percent the same as angle?
No. 45° is 100 %, and 90° (vertical) is infinite. Small slopes are close: 5 % ≈ 2.9°.
More calculators
Estimates only — check quantities with your supplier and local building code before you order.