Rainwater Harvesting
About Rainwater
What this tool does
Plumbing tools calculate pipe volume, water pressure at a given head, drain slope requirements, pipe sizing for flow rate, water heater capacity, and sewer pipe diameter.
Why use this tool
Plumbing installations must meet code requirements for slope, flow, and pipe size. Under-sizing a drain pipe causes backups; over-sizing wastes materials. These calculators help you spec the right components before you start digging.
How it works
Pipe volume uses the cylinder formula (pi x r^2 x length). Water pressure converts head (height of water column) to PSI using the factor 0.433 PSI per foot. Drain slope tools apply the code-minimum gradient (typically 1/4 inch per foot for residential).
Pro tip
For residential drain lines, 1/4 inch of slope per foot is the minimum, but 1/8 inch per foot is acceptable for pipes 3 inches and larger. Always check your local plumbing code.
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