Pipe Slope Calculator
Calculate pipe or drainage slope from a vertical fall and horizontal run measured in the same unit.
Written and checked by TheToolNet Editorial Team · Last reviewed: September 20, 2026 · Editorial method
Calculate pipe fall and grade
Pipe slope formula
fall ÷ horizontal run × 100 = grade %
A 2-unit fall over 100 horizontal units is a 2% downward grade, written 1:50. Keep the input units identical. This geometry also applies to a simple drainage-slope calculation.
Do not use grade alone to size drainage
Acceptable slope depends on pipe diameter, material, flow, fittings, venting, cleaning access, and the plumbing or civil standard that governs the project. This calculator does not determine capacity or code compliance.
For arbitrary inclines, use the slope percentage calculator.