How it works
Enter the rise (how much the ground or pipe drops) and the run (the horizontal distance) in any units. The calculator returns percent grade, the angle in degrees, the ratio and the drop per foot.
Percent grade is rise divided by run times 100, which is different from degrees: a 100% grade is 45°. Contractors usually talk in percent or inches per foot; a 2% grade is about 1/4 inch per foot.
For drainage, the International Residential Code (R401.3) requires ground to slope away from foundations at least 6 inches within the first 10 feet, a 5% grade. Lawns drain well at 1% to 2%, and drain pipes are typically laid at 1/8 to 1/4 inch per foot.
Formula
Grade % = rise ÷ run × 100. Angle = arctan(rise ÷ run). Drop per foot (in) = rise ÷ run × 12.
Questions people ask
How much should my yard slope away from the house?
At least 6 inches over the first 10 feet (5%) under the IRC. Where lot lines or obstacles prevent that, swales or drains can be used instead.
What is the difference between percent grade and degrees?
Percent is rise over run times 100; degrees is the angle itself. 10% is about 5.7°, 50% is about 26.6° and 100% is 45°.
What slope does a drain pipe need?
Commonly 1/4 inch per foot (about 2%) for pipes 2.5 inches and smaller and at least 1/8 inch per foot (1%) for 3 to 6 inch pipes, per plumbing codes.
What is the maximum slope for a wheelchair ramp?
ADA guidelines allow a maximum of 1:12, about 8.33%, with a rise of no more than 30 inches per ramp run before a landing.