Pipe Sizing Calculator
Enter your fixture counts and longest pipe run to get the correct supply line diameter per IPC Table 604.3 / 604.4. Used by licensed plumbers for rough-in sizing.
Fixture counts
How does IPC pipe sizing work?
- Fixture units (FU). The International Plumbing Code assigns each fixture a demand load in "fixture units." A toilet draws 3 FU, a washing machine 4 FU, a kitchen sink 2 FU. Fixture units model simultaneous demand probability — not raw flow rate.
- Run length adjustment. Longer pipe runs have higher friction losses, so the same fixture unit load requires larger pipe. IPC Table 604.4 provides three columns: runs ≤40 ft, ≤80 ft, and ≤160 ft. Enter your longest run from the meter to the farthest fixture.
- Material note. Copper, PEX, and CPVC have similar inside diameters at standard sizes, so the code sizing is equivalent across materials. The calculator notes the common trade name (Type L copper, PEX-A/B, CPVC SCH 40) but the nominal size is the same.
- Branch sizes. Per IPC Section 604.5, individual fixture branches are sized separately — most single fixtures require ½" minimum; washing machines require ¾". The calculator outputs branch recommendations alongside the main line size.
When should you consult a licensed plumber?
This calculator uses IPC Table 604 directly and is appropriate for standard residential rough-in planning. Commercial buildings, fire-sprinkler integration, booster pump systems, or any jurisdiction using UPC (Uniform Plumbing Code) instead of IPC requires a licensed plumber's sealed drawings. Most jurisdictions require a permit and inspection for any supply-line rough-in.
Code references: methodology page.
What else do people ask about pipe sizing?
What is a "fixture unit" in pipe sizing?
A fixture unit (FU) is the demand load the International Plumbing Code assigns to each fixture to model simultaneous-use probability, not raw flow rate. A toilet is 3 FU, a washing machine is 4 FU, and a kitchen sink is 2 FU.
Does the pipe material change the sizing?
No. Copper, PEX, and CPVC have similar inside diameters at standard sizes, so the code sizing from IPC Table 604 is equivalent across materials. The calculator notes the common trade name for each material but keeps the same nominal size.
Why does a longer pipe run need a larger pipe?
Longer runs have higher friction losses, so the same fixture-unit load needs larger pipe to deliver adequate pressure. IPC Table 604.4 accounts for this with three run-length columns: up to 40 ft, up to 80 ft, and up to 160 ft, measured from the meter to the farthest fixture.
What size branch line does a single fixture need?
Per IPC Section 604.5, individual fixture branches are sized separately from the main line. Most single fixtures need a 1/2" minimum branch, while washing machines need 3/4".
Does this calculator work for commercial buildings?
No. It applies IPC Table 604 directly, which is appropriate for standard residential rough-in planning. Commercial buildings, fire-sprinkler integration, booster pump systems, or jurisdictions using the Uniform Plumbing Code instead need a licensed plumber's sealed drawings.
Sources
Want the real number for your house? A licensed plumber gives you a written estimate by phone — free, no obligation.