Drain Pipe Slope Calculator
Work out how far a drain pipe needs to fall over its length, or check the slope you already have.
Pipe slope calculator
How it is calculated
Slope is how far the pipe drops for each unit of length. Multiply the run by the slope to get the total drop.
Total drop = run × slopeExample: a 40 ft run at 1/4 in per foot drops 40 × 1/4 = 10 in. As a percentage, 1/4 in per foot is about 2.08%.
Codes differ by place and pipe size, so treat the verdict as a guide and confirm it with your local plumbing code.
Common questions
What slope should a drain pipe have?
Many plumbing codes call for 1/4 inch per foot for drain pipes up to about 2 1/2 inches, and 1/8 inch per foot for larger pipes. Your local code decides.
How do I convert inches per foot to a percentage?
Divide the inches by 12 and multiply by 100. 1/4 in per foot is 0.25 ÷ 12 × 100 = 2.08%.
Can a drain pipe be too steep?
Very steep runs are fine for many jobs, but some codes and installers prefer to stay near the standard range. Check local rules.