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Plumbing Pipe Sizing Calculator

Fixture counts → fixture units → peak GPM → recommended pipe diameter.

Where this fits

📦 Business & Seller OpsGoing 1099FreelancersFounders

This tool lives inside Going 1099 and is most useful for freelancers and founders.

Corp Tax Rate21%
SE Threshold$400
FICA Cap 2024$168,600

Fixtures

System

Recommended size
1.25"
PEX pipe
Peak demand
22.0 GPM
10.5 fixture units
Supply pressure
60 PSI
at meter
Residual pressure
~60 PSI
at end of run
1

Fixture units (supply)

FU = Σ(fixture type × count) per IPC table

= 10.5 fixture units

IPC Table E103.3(2) — supply fixture unit values

2

Probable demand (Hunter's method)

GPM = lookup(fixture units)

= 22.0 GPM

Hunter's method converts fixture units to peak probable flow

3

Recommended pipe size

Minimum diameter to carry demand GPM at ≤8 fps velocity

= 1.25" PEX pipe

IPC recommends max 8 fps for supply piping

4

Residual pressure

= ~60 PSI at end of run

Fixtures require minimum 8–25 PSI depending on type

Key insight

This is a simplified Hunter's method estimate. Actual sizing requires the full IPC/UPC fixture unit tables, equivalent length calculations for fittings, and local water pressure testing. For permitted work, have a licensed plumber verify sizing calculations.

Use this result in →

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