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Slope Calculator
Slope is one number with three common languages: percent, degrees and ratio. Enter the rise and the run in the same unit — inches, feet, meters, anything — and this calculator gives you all three so you can match whatever your plans, code or spec sheet use.
Results update as you type. Estimates only — confirm final quantities before ordering.
The formula
Angle = arctan(Rise ÷ Run)
Ratio = 1 : (Run ÷ Rise)
All three forms describe the same steepness. Percent is common in civil work and drainage, degrees in machining and some trade specs, and the ratio form (1 : 12, 1 : 4) in accessibility codes and roofing. Rise and run must be measured in the same unit, and the run is always the horizontal distance, not the length of the sloped surface.
Worked example
Example: a ramp that rises 3 ft over a horizontal run of 12 ft.
- Slope: 3 ÷ 12 × 100 = 25.00%
- Angle: arctan(0.25) = 14.04°
- Ratio: 1 : (12 ÷ 3) = 1 : 4
Reference chart
| Slope % | Angle | Ratio (1 : X) |
|---|---|---|
| 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% | 45.00° | 1 : 1 |
Frequently asked questions
What is the maximum slope for a wheelchair ramp?
The ADA standard is 1 : 12 (8.33%, 4.76°) maximum for new construction, with landings required for longer runs. Always confirm against your local code, which may be stricter.
What slope do I need for drainage?
Patios, walks and slabs should shed water at about 1–2% (roughly 1/8 to 1/4 inch per foot). Lawns drain at similar gentle grades; buried drain pipe typically needs at least 1% (about 1/8 inch per foot) to flow.
How do I measure rise and run on site?
Stretch a level line (or use a long level) from the high point, measure the horizontal distance for the run, then measure straight down from the line to the low point for the rise. Rise and run must use the same unit.
Is slope the same as roof pitch?
They describe the same idea differently. Pitch is stated as rise per 12 units of run (a 6/12 pitch), while slope percent is rise ÷ run × 100 — so a 6/12 pitch equals a 50% slope. Our Roof Pitch Calculator handles the roofing convention directly.
Related calculators
- Roof Pitch Calculator — Pitch (x/12), angle, slope percent and rafter factor.
- Gravel Calculator — Gravel in cubic yards and tons, by depth and density.
- Concrete Calculator — Cubic yards and bag counts for slabs, patios and pads.
Sources & method: Standard trigonometry (arctangent); Omni Calculator — Slope Calculator; ADA Standards §405 (ramp slope 1:12 maximum).