Water Supply & Pipe Sizing
The water-supply and pipe-sizing engine: supply pipe size from water-supply fixture units (WSFU → peak GPM → diameter band), water pressure and elevation head (psi = ft ÷ 2.31) with a PRV target, friction / pressure loss per 100 ft, water volume held in the pipe (gal = 0.0408 × diameter² × length) and time-to-hot, a bucket-test flow rate, and peak demand from WSFU. Sizing values are labeled planning bands — your local code and a licensed plumber set the design.
Local plumbing code governs: This sizing follows standard reference conventions (IPC / UPC / NFPA-54-style tables). Your local plumbing code and inspector govern — sizing methods, materials and permit rules vary by jurisdiction. Confirm the design with a licensed plumber and pull the required permit before you build.
Supply Pipe SizeFind the water supply pipe size for your house from total fixture units. WSFU becomes a peak-demand GPM band, then the smallest copper line that carries it.Pressure & HeadEstimate the water pressure left at a fixture after elevation and friction. Every foot of lift costs 1 psi ÷ 2.31, so upper floors see weaker flow.Friction LossEstimate friction pressure loss over a pipe run: loss per 100 ft times the developed length. See how long runs and high flow cut fixture pressure.Pipe Volume & Time-to-HotCalculate the water held in a pipe (gal = 0.0408 × d² × L) and how long it takes to clear at a given flow — your wait for hot water and the water it wastes.Flow Rate (Bucket Test)Measure your real water flow with a bucket test: gallons ÷ seconds × 60 = GPM. Check a shower, faucet or hose against typical flow rates in seconds.Peak Demand GPMConvert total water-supply fixture units to a peak demand in GPM using a labeled Hunter-curve band — the number that sizes your meter, service line and main.
Every Water Supply & Pipe Sizing tool is calculated server-side — visible immediately — with its formula, a worked example and a reference table, and works on the prices you enter. Background reading is in the guides.