Pipe Sizing Quick Reference (IPC Table E103.3)

IPC Table E103.3 gives the minimum supply pipe diameter for a given fixture unit (FU) load. This is the go-to reference for sizing water service and distribution piping in residential and light commercial work.

Minimum Pipe Size by Fixture Units

Fixture Units (FU)	Minimum Pipe Size
1 FU	1/2 inch
2 to 4 FU	3/4 inch
5 to 8 FU	1 inch
9 to 14 FU	1-1/4 inch
15 to 24 FU	1-1/2 inch
25 to 42 FU	2 inch
43 to 60 FU	2-1/2 inch
61 to 96 FU	3 inch
97 to 256 FU	4 inch

Common Fixture Unit Values (IPC Table 604.3)

Fixture	Supply FU
Toilet (tank type)	3
Lavatory (bathroom sink)	1
Bathtub	2
Shower	2
Kitchen sink	2
Dishwasher	1.5
Clothes washer	2
Hose bibb (outdoor faucet)	2.5
Drinking fountain	0.5

How to Use the Table

1. List all fixtures on the pipe segment. Include every fixture downstream of the point you are sizing.
2. Sum the fixture units. Use IPC Table 604.3 values for each fixture type.
3. Look up the pipe size. Find the row that equals or exceeds your FU total and read the pipe size.
4. Apply pressure and velocity checks. The table assumes standard residential pressure (40-80 psi). For long runs, verify velocity stays under 8 fps (residential) or 10 fps (commercial) to prevent water hammer.

Material Notes

The IPC Table E103.3 sizing applies to copper (Type L and M), CPVC, and PEX piping. Galvanized steel requires slightly larger sizes due to rougher interior walls and corrosion-related flow restriction over time.

PEX is the most common retrofit choice today due to flexibility, freeze resistance, and cost. PEX-A (Uponor, Rehau) has the best expansion characteristics; PEX-B and PEX-C are lower cost and widely accepted by code.

Reference

IPC Table E103.3(1), 2021 edition -- Demand Versus Required Size of Water-Service and Water-Distribution Pipe.