Drainage Slope Calculator

Overview

Divides elevation drop by run length to report percent slope and inches of fall per foot, and adds staking supplies.

Assumptions

• Run is horizontal distance, not pipe length along a slope.
• Inputs are measured between the high point and outlet.

Worked example

A 50-ft run with 6 in of drop is (0.5 ÷ 50) × 100 = 1% and 6 ÷ 50 = 0.12 in per foot.

Common mistakes

• Mixing inches and feet in the slope calculation.
• Measuring from finished grade at one end and trench bottom at the other.

Limitations

It does not determine whether the receiving outlet can accept water.

Safety and local requirements

Protect trip hazards from strings and stakes; confirm discharge and grading rules with the local authority.

Sources

• EPA — Soak Up the Rain