CalcCoverageThree ways to say the same slope
Slope is one idea wearing three costumes. Percent is rise over run times 100 — the language of roads and drainage. Degrees is the angle from horizontal — the language of ramps and machinery. The ratio, written 1 in X, says how far you travel horizontally for one unit of climb — the language of accessibility standards and plumbing falls.
Slope % = rise ÷ run × 100 · Angle = arctan(rise ÷ run) · Ratio = 1 in (run ÷ rise)
Example: a pipe run that rises 3 in over 12 in is a 25% slope, at 14.04 degrees, a ratio of 1 in 4 — steep for a pipe, which is the sort of thing this conversion exists to catch.
Slopes you will meet
| Use | Typical slope |
|---|---|
| Drainage pipe fall (minimum) | 2% — 1/4 in per ft (1 in 48) |
| Patio / paving fall away from a house | 1.5–2% (1 in 50–65) |
| Wheelchair ramp (maximum, US ADA) | 8.33% — 1 in 12 |
| Driveway (comfortable maximum) | 12–15% |
| 6/12 roof pitch | 50% — 26.57 degrees |
Percent and degrees are not interchangeable, and confusing them is the classic slope error: a 100% slope is 45 degrees, not vertical, and a 10% grade is a gentle 5.7 degrees despite sounding dramatic. This converter is deliberately nothing but the conversion, done exactly — for roof work the companion roof pitch calculator adds rafter lengths and slope factors.