Slope & Grade Calculator
Calculate slope, grade percentage, ratio, and angle from any two known values. Includes ADA and drainage compliance checks.
About This Tool
When to Use This Calculator
Use the Slope and Grade Calculator when planning drainage around a foundation, grading a yard, designing a wheelchair ramp to ADA standards, determining roof pitch, or laying pipe with proper fall. Any project where you need to express an incline as a percentage, ratio, angle in degrees, or simple rise-over-run benefits from this tool, especially when you need to verify compliance with building codes or accessibility standards.
How It Works
Enter any two known values — rise and run, rise and angle, or run and angle — and the calculator computes all the other representations of that slope: percentage grade, ratio (e.g., 1:12), degrees, and the missing rise or run dimension. It also checks your slope against common code requirements, including ADA ramp maximums, minimum drainage grades for foundations, and typical plumbing pipe slopes, flagging whether your design is compliant.
Tips for Best Results
- For foundation drainage, aim for a minimum 5% grade (about 6 inches of drop over 10 feet of run) within the first 10 feet away from the house to keep water moving away from the structure.
- ADA-compliant ramps must not exceed a 1:12 slope (8.33%) and require level landings at least 60 inches long at the top, bottom, and every 30 feet of horizontal run.
- Drain pipe for residential plumbing typically requires 1/4 inch of fall per foot of run (about 2% grade) for proper flow without sediment buildup or clogs.
- When measuring an existing slope in the field, use a long straight board and a level rather than trying to sight along the ground — even small undulations in the terrain can throw off your reading significantly.