Tools you might need next
Calculate Reynolds number to characterize flow regime in a pipe. Free reynolds number calculator for reynolds, number, and more.
Calculate average flow velocity from volumetric flow rate and pipe area. Free pipe flow velocity tool for pipe, flow, and more.
Solve for unknown pressure using Bernoulli equation between two points. Free bernoulli equation solver solver for bernoulli, equation, and more.
Each fixture type contributes drainage or supply fixture units. Supply sizing uses water supply fixture units (WSFU).
Total DFU = Σ Fixture Unit Values (IPC Table 604.3)Peak demand GPM estimated from total WSFU — not all fixtures flow simultaneously at full rate.
GPM ≈ lookup from WSFU curve (Hunter's curve approximation)1/2″ ~ 3–5 GPM; 3/4″ ~ 6–10 GPM; 1″ ~ 10–16 GPM at acceptable velocity for residential.
Select pipe size where velocity ≤ 5–8 fps at peak GPMUpdated: July 2026
Typical 3-bed home ~25 WSFU peak ~8 GPM. 3/4″ main minimum; 1″ preferred for long runs or high demand.
Lav + tub/shower + toilet branch: 1/2″ adequate for individual bathroom group if length < 30 ft.
Extend 3/4″ trunk; 1/2″ branches to new lav and hose bib. Verify existing main capacity.
Determine minimum water supply pipe diameter based on fixture unit count and peak demand flow rate. Enter number of fixtures and developed length to select copper, CPVC, or PEX size per IPC/UPC fixture unit methods.