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Plumbing Reference
Pipe sizing · Fixture units · Rough-in dims · Materials
Fixture Drain Units (DFU) & Sizing
| Fixture | DFU | Min. Supply | Min. Drain |
|---|---|---|---|
| Lavatory (sink) | 1 | 3/4" | 1-1/2" |
| Kitchen Sink | 2 | 3/4" | 1-1/2" |
| Bathtub | 2 | 1/2" | 1-1/2" |
| Shower (single head) | 2 | 1/2" | 2" |
| Toilet (flush tank) | 3 | 3/8" | 3" |
| Washing Machine | 3 | 3/4" | 2" |
| Dishwasher | 2 | 1/2" | 1-1/2" |
| Floor Drain (2") | 1 | — | 2" |
| Floor Drain (3") | 2 | — | 3" |
| Utility Sink | 3 | 3/4" | 1-1/2" |
| Hose Bibb | 3 | 1/2" | — |
Drain Stack Sizing (DFU)
- Up to 3 DFU → 1-1/2" drain
- Up to 6 DFU → 2" drain
- Up to 20 DFU → 3" drain
- Up to 160 DFU → 4" drain
Vent Sizing Rule of Thumb
- Vent ≥ 1/2 drain pipe diameter
- Min. vent size: 1-1/4"
- Stack vent: same as drain stack
- Max vent length varies by code
Drain Slope
- 2" & smaller: 1/4" per foot min
- 3" & larger: 1/8" per foot min
- Max slope: 1/2" per foot (steeper = code specific)