Pipe sizing cheat sheet
Fixture flows and pipe capacities on one page — the quick reference to keep in the truck. Free to use and print.
A pipe sizing cheat sheet is a quick-reference that maps common fixtures to their flow in gallons per minute (GPM) and pipe sizes to their approximate flow capacity, so you can size a water line at a glance. Use it to estimate peak demand, pick a starting pipe size, and sanity-check a run in the field. The figures below are general reference values — handy for a fast estimate, but not a substitute for your local plumbing code or a full fixture-unit calculation. When it counts, run the exact numbers with the pipe sizing calculator and confirm against code.
Common fixture flow rates (GPM)
Add up the fixtures that can realistically run at the same time to estimate peak demand for a run.
| Fixture | Typical flow (GPM) |
|---|---|
| Bathroom (lavatory) faucet | 1.5 |
| Kitchen faucet | 1.5 – 2.2 |
| Shower head | 2.0 – 2.5 |
| Toilet (tank refill) | 2 – 3 |
| Bathtub | 4 |
| Dishwasher | 1 – 2 |
| Clothes washer | 4 |
| Hose bib / sillcock | 5 |
Pipe size to flow capacity
Approximate residential capacity at normal pressure, keeping velocity in a safe range. Material, pressure, and run length all shift these, so treat them as a starting point.
| Nominal size | Copper (type L) | PEX |
|---|---|---|
| 1/2 in | ~3 – 5 GPM | ~2 – 4 GPM |
| 3/4 in | ~8 – 12 GPM | ~6 – 10 GPM |
| 1 in | ~16 – 22 GPM | ~13 – 18 GPM |
| 1¼ in | ~25 – 35 GPM | ~22 – 30 GPM |
| 1½ in | ~40 – 50 GPM | ~34 – 44 GPM |
PEX runs a little lower than copper at the same nominal size because its inside diameter is smaller. Check exact flow with the water flow rate calculator.
Water service rule of thumb
- 3/4 in — a small home, a few fixtures, short run.
- 1 in — a typical single-family water service.
- 1¼ – 1½ in — larger homes, long runs, or higher simultaneous demand.
- Size up one step for long runs or low incoming pressure — friction loss eats flow. See how to size a water line.
Gas pipe — quick notes
Gas sizing depends on total appliance BTU, pipe length, and pipe type, so it does not reduce to one clean chart. The short version: size to the longest run and the total connected BTU load, and never eyeball it. Run your exact case through the gas line sizing calculator, and always confirm against local fuel-gas code. The underlying trade is standard piping practice.
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Open the PlumbCalc calculators Home plumbing help hubPipe sizing cheat sheet — FAQ
What is a pipe sizing cheat sheet?
A quick-reference mapping fixtures to their GPM and pipe sizes to their approximate capacity, so you can size a water line at a glance — a starting point, not a replacement for code.
What size water line do I need?
Add the peak GPM of fixtures that run at once, then pick a pipe that meets it. Roughly, 3/4 in for a small branch, 1 in for a typical service — but length and pressure shift it.
How many GPM can a 3/4 inch pipe handle?
Roughly 8 to 12 GPM for a typical residential run at normal pressure — an approximate range. Confirm your exact case with the calculator and local code.
Is this a substitute for code?
No — these are general reference figures. Always confirm the final size against the plumbing code that applies to your job.