Grade & Slope Calculator
Work out the slope of a driveway, ramp, roof, drain line or road — as a percent grade, an angle, and a ratio like 1:12 — with a picture of the triangle and the run, rise and length that go with it.
Common grades for reference
| Grade | What it is |
|---|---|
| 2% | Minimum for positive drainage |
| 5% | Gentle road / gentle ramp |
| 8.33% | ADA accessible ramp (1:12) max |
| 10% | Steep driveway |
| 25% | Very steep |
One Slope, Three Ways to Say It
Whether you are pitching a driveway to drain, checking a wheelchair ramp, laying out a roof, or grading a yard, it all comes down to slope — and everyone writes it differently. A ramp is called out as 1:12, a driveway as a percent, a roof as a pitch. They all describe the same triangle of rise over run. This calculator shows the grade percent, the angle and the ratio at once, draws the triangle, and gives the slope length you actually measure on site.
One thing that trips people up: percent grade and angle are not the same number. A 100% grade is not a cliff — it is 45 degrees, where rise equals run. Percent keeps climbing toward infinity as the slope nears vertical, while the angle stops at 90.
Grades Worth Knowing
| Grade | Where you see it |
|---|---|
| 1 to 2% | Minimum drainage slope so water runs off |
| 5% | A gentle road or a comfortable ramp |
| 8.33% (1:12) | Maximum slope for an ADA accessible ramp |
| 10 to 15% | Steep driveway territory |
| 25%+ | Very steep – getting into stairs and walls |
Driveways, Ramps, Roofs and Drainage
For a driveway, aim for enough slope to drain (1 to 2% across, away from the house) but rarely more than about 15% along its length. A ramp for accessibility cannot exceed 8.33%, or 1 foot of rise for every 12 feet of run. A roof is usually given as a pitch like 4:12 — that is rise in inches per 12 inches of run, which this tool reads directly as a ratio. And drainage almost always wants that gentle 2% so water moves without pooling or scouring.
Frequently Asked Questions
What does 1:12 mean?
One unit of rise for every twelve units of run – the maximum for an ADA ramp. It works out to an 8.33% grade, or about 4.76 degrees.
Is the slope length the same as the run?
No. The run is the flat, horizontal distance; the slope length is the actual distance along the surface (the hypotenuse) and is always a bit longer. That is the number you need for ramp length, railing or decking.
How does roof pitch fit in?
Roof pitch is rise over a 12-inch run – a 6:12 roof rises 6 inches per foot, which is a 50% grade and about 26.6 degrees. Enter rise 6 and run 12 to see it.
Related calculators
- DIY & Construction calculators — the full DIY library.
- Stormwater Runoff Calculator — size drainage for the water your grade sheds.
- Open-Channel Flow Calculator — how channel slope drives flow.
- Excavation Calculator — earthwork to cut a grade in.