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Free Drain Slope Calculator
Calculate the total drop for a drain pipe run based on the horizontal run length and slope in inches per foot. The International Plumbing Code (IPC) requires a minimum slope of 1/4 inch per foot for 3-inch and smaller drains. Results show total drop in inches and feet, plus slope percentage.
Frequently asked questions
What is the correct slope for a drain pipe?
The IPC requires a minimum slope of 1/4 inch per foot (2%) for 3-inch and smaller drain pipes. Larger pipes (4 inches and above) require a minimum of 1/8 inch per foot (1%).
How do I calculate drain pipe drop?
Drop = Run length (ft) × Slope (in/ft). For example, a 20-foot run at 1/4 inch per foot drops 5 inches total.
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