Tools you might need next
Calculate water flow rate GPM from pipe velocity and diameter. Size pipes and estimate fixture supply capacity for plumbing and irrigation design.
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.
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.