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Size water supply pipes by fixture units and flow rate. Calculate copper and PEX pipe diameter for residential plumbing per IPC fixture unit tables.
Calculate water pressure loss in pipes from flow, length, and diameter. Estimate PSI drop for residential plumbing and irrigation system design.
Calculate drain pipe slope per IPC code. Enter pipe diameter and run length to get minimum and recommended fall in inches per foot for waste lines.
Area = π × (ID/2)². Factor 0.408 converts sq in × fps to GPM.
GPM = Velocity (fps) × Area (sq in) × 0.408High velocity causes noise and erosion. Low velocity in drains allows solids deposition.
Recommended: 5–8 fps supply; 2–4 fps drainageIterative relationship between flow, velocity, and friction — higher flow increases pressure loss.
GPM from Hazen-Williams given available PSI and pipe geometryUpdated: July 2026
ID 0.824″ → ~9.5 GPM capacity. Adequate for single shower (~5 GPM) plus lav if pressure stable.
Limit velocity to reduce friction on long run. 1″ at 5 fps ≈ 15 GPM for multi-zone manifold.
Residential sprinkler design uses specific GPM per head — professional calc required beyond this tool.
Calculate volumetric flow rate in gallons per minute from pipe internal diameter and water velocity. Enter pipe size and velocity (or pressure and length) to verify supply capacity meets fixture and irrigation demand.