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About this tool
Convert slope between percent grade, degrees, 1-in-X ratio, inches per foot and roof pitch for ramps, drains and roofs.
This 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.
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Percent, degrees, ratio, in/ft, mm/m and roof pitch from one entry, so nothing gets converted twice.
Enter the length of the ramp or pipe and get the rise to mark, in the same unit.
ADA ramp and cross-slope limits and drain minimums shown as ratio, percent and 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.
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.
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.
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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