Drainage Slope Calculator
Convert between run length, fall (drop), percent slope, and inches-per-foot, with a verdict for hardscape drainage.
Limitations: Two-point slope only — does not evaluate crowned, cross, or compound slopes. Verdict thresholds apply to hardscape drainage, not roofing or pipe flow.
What to do next: Residential patio / driveway minimum is 1% (1/8 in per ft) away from the house; 2% (1/4 in per ft) is the comfortable default. ADA accessible route max is 5% (1:20) for walkways, 8.33% (1:12) for ramps.
Planning guide only. For pipe flow slopes, sanitary drain codes, or structural grading, follow the applicable plumbing / civil code.