What it calculates
Calculate required fall over a drain run.
Drain Slope / Pitch Calculator
Calculate required vertical fall from drain length and slope.
Planning and estimating aid only. Verify project requirements, manufacturer instructions, adopted codes, permits, and field conditions before performing regulated work.
Plumbing planning
How to Use This Calculator
Use the field units shown below, then compare your result with the worked example. Measure the available start and end elevations before relying on the result.
How the calculation works
Total fall = run length × slope in inches per foot.
What the result means
The result is the elevation difference required from the beginning to the end of the entered run.
Convert an entered slope into total fall
A 40-foot run at an entered slope of 0.25 inches per foot has 40 × 0.25 = 10 inches of fall, or about 0.83 feet. The example shows unit conversion; it does not establish which slope is permitted for a drain.
Contractor tip: Measure the available start and end elevations before relying on the result. A computed fall can show that the route will not fit, but it does not by itself validate an installation.
Verify the final quantity
The slope field is inches of fall per foot of run, not a percentage. The tool does not check pipe size, discharge, venting, fittings, support or local plumbing requirements.
Good practice: Compare the calculated quantity with plans, specifications, product packaging and current field conditions before purchasing material.