Slope Percent Degree Converter
Convert slope between percent grade, degrees, 1-in-X ratio, inches per foot and roof pitch for ramps, drains and roofs.
About this tool
Slope Percent Degree Converter
Convert slope between percent grade, degrees, 1-in-X ratio, inches per foot and roof pitch for ramps, drains and roofs.
The Slope Percent Degree Converter takes a slope written in any one notation and gives you all the others: percent grade, angle in degrees, the 1-in-X ratio used in building codes, inches per foot, millimetres per metre and roof pitch in twelfths. It works from the single underlying ratio — percent grade is rise divided by run times 100, and the angle is the arctangent of that same ratio — which is why 100% grade is 45 degrees rather than vertical. It also gives the actual fall over a run you enter, the number you mark on a wall or set a pipe to.
How to use Slope Percent Degree Converter
- 1
Open Slope Percent Degree Converter on AltFTool — it loads instantly in your browser.
- 2
Under 'What do you have?' pick Percent grade (%), Degrees (°), Ratio 1 in X, Inches per foot, Millimetres per metre, Per mille or Rise and run.
- 3
Type the value, or tap a preset such as 'ADA ramp 1:12' or 'Drain 1/4 in per ft', then set 'Run length (any unit)' under Fall over a run.
- 4
Read the percent grade with the angle, the 1 in X ratio, in/ft, mm/m, roof pitch in 12 and the ADA 1:12 check, then press Copy result.
Why use Slope Percent Degree Converter
Every notation at once
Percent, degrees, ratio, in/ft, mm/m and roof pitch from one entry, so nothing gets converted twice.
Fall over a real run
Enter the length of the ramp or pipe and get the rise to mark, in the same unit.
Code thresholds beside your number
ADA ramp and cross-slope limits and drain minimums shown as ratio, percent and degrees.
Common use cases
- Check that a wheelchair ramp drawn at 6% is inside the ADA 1:12 (8.33%) maximum running slope.
- Set a waste pipe to the 1/4 inch per foot fall a small drain needs and see it as 20.8 mm per metre for a metric level.
- Translate a surveyor's 12% grade into degrees for a machine that only accepts an angle.
Frequently asked questions
What is 100% slope in degrees?
45 degrees. A 100% grade means the rise equals the run, and the angle is arctan(1) = 45 degrees. Percent grade and degrees only track each other near zero — they are not interchangeable, and a vertical face has an infinite percent grade.
What is a 1 in 12 slope as a percentage?
8.33%, which is 4.76 degrees. That is the maximum running slope the ADA Standards allow for a ramp (section 405.2), meaning 1 unit of rise for every 12 units of run — a 250 mm step needs 3 m of ramp.
What slope should a drain pipe have?
The International Plumbing Code Table 704.1 sets a minimum fall of 1/4 inch per foot (2.08%, about 1 in 48) for drains 2 1/2 inches and smaller, and 1/8 inch per foot (1.04%, about 1 in 96) for 3 to 6 inch drains. Too little slope leaves solids behind; far too much lets water run away from them.
How do I convert percent grade to degrees?
Divide the percent by 100 and take the arctangent: degrees = atan(percent / 100). So 6% becomes atan(0.06) = 3.43 degrees, and 25% becomes 14.04 degrees. To go the other way, degrees to percent, use tan(angle) x 100.
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