Slope Converter
Enter rise and run to get the slope as a percentage, in degrees, as a ratio and as rise per metre.
Inputs
Result
Formula
| Slope | i = rise ÷ run |
| Percentage | slope % = i × 100 |
| Angle | θ = arctan(i) |
| Ratio | 1 : n where n = 1 ÷ i |
| Slope length | L = √(rise² + run²) |
A 1 m rise over 10 m run: 10% slope, 5.71°, ratio 1:10, 100 mm per metre, and a slope length of 10.05 m.
Slope conversion table
| Slope | Angle | Ratio | Rise per metre | Typical use |
|---|---|---|---|---|
| 0.5% | 0.29° | 1:200 | 5 mm | Surface drainage |
| 1% | 0.57° | 1:100 | 10 mm | Gutters and eaves |
| 2% | 1.15° | 1:50 | 20 mm | Flat roof falls |
| 3% | 1.72° | 1:33.3 | 30 mm | Structural falls |
| 5% | 2.86° | 1:20 | 50 mm | Profiled metal roofs |
| 10% | 5.71° | 1:10 | 100 mm | Max. accessible ramp |
| 20% | 11.31° | 1:5 | 200 mm | Asphalt shingle roofs |
| 33% | 18.26° | 1:3 | 330 mm | Plain tile roofs |
| 50% | 26.57° | 1:2 | 500 mm | Steep pitched roofs |
| 100% | 45.00° | 1:1 | 1000 mm | 45° pitched roof |
FAQ
Should I use percent or degrees?
Percent (or per mille) suits earthworks, roads and drainage because you can compute fall directly from horizontal distance, which is how you set out. Degrees suit steelwork and machine installation where the angle between members matters. Roofs are usually given as a ratio. The conversion is percentage = tan(angle) × 100, so 45° is 100%, not 90%.
What roof slopes are typical?
Flat roofs are graded at least 3% structurally or 2% with a screed, and gutters need at least 1% longitudinal fall. Tiled roofs depend on the covering: plain tiles about 20-50%, asphalt shingles at least 20%, profiled metal at least 5%. Insufficient fall on flat roofs is the single biggest cause of leaks.
What is the most common setting-out mistake?
Using the slope length as the run. Measuring 10 m along the slope when the horizontal distance is only 9.96 m makes the gradient read high. Measure the run horizontally with a level or total station, or derive l = rise ÷ i first. Also check that drainage falls toward the outlet, not away from it.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.