Pipe Sizing Reference
Nominal pipe sizes, outer/inner diameters, and typical flow rate ranges for copper schedule 40 pipe. Material comparison for supply and DWV applications. Verify with IPC or UPC as adopted locally.
Nominal Pipe Sizes — Schedule 40
| Nominal Size | OD (in) | ID (in) | Wall (in) | Flow GPM (residential) | Flow GPM (commercial) | Common Uses |
|---|---|---|---|---|---|---|
| 1/2" | 0.84" | 0.622" | 0.109" | 1-8 | 1-10 | Branch lines to fixtures, shower heads, small faucets |
| 3/4" | 1.05" | 0.824" | 0.113" | 8-15 | 10-20 | Main branch lines, hose bibs, water heater connections |
| 1" | 1.315" | 1.049" | 0.133" | 15-25 | 20-35 | Main supply line for most homes, main branch lines |
| 1-1/4" | 1.66" | 1.38" | 0.14" | 25-40 | 35-55 | Drain lines, main supply for larger homes |
| 1-1/2" | 1.9" | 1.61" | 0.145" | 40-60 | 55-80 | Drain/vent stacks, commercial branch mains |
| 2" | 2.375" | 2.067" | 0.154" | 60-100 | 80-130 | Main drain lines, commercial mains, irrigation mains |
| 3" | 3.5" | 3.068" | 0.216" | N/A | 200-300 | Soil stacks, building drains, commercial supply mains |
| 4" | 4.5" | 4.026" | 0.237" | N/A | 400-500 | Building drain to sewer, large commercial supply |
Nominal pipe size does not equal actual OD or ID. A "1/2 inch" pipe has an OD of 0.840". Always use actual dimensions for fitting compatibility.
Schedule 80 has a thicker wall and smaller ID than Schedule 40 at the same nominal size. Sch 80 is used in higher-pressure applications. OD is identical — fittings are interchangeable within the same nominal size.
Drain/waste/vent (DWV) pipes use gravity flow — sizing is based on drainage fixture units (DFUs), not pressure. Supply lines use pressure flow. Never interchange DWV-rated and supply-rated materials.
Pipe Material Comparison
| Material | Max Pressure | Max Temp | Lifespan (est.) | Notes |
|---|---|---|---|---|
| Copper (Type L) | 800 | 250°F | 50+ | Standard residential supply; antimicrobial; soldered fittings |
| Copper (Type M) | 600 | 250°F | 50+ | Thinner wall than Type L; some codes restrict to above-ground only |
| PEX-A | 160 | 200°F | 40-50 | Most flexible PEX; expansion fittings; freeze-resistant |
| PEX-B | 160 | 200°F | 40-50 | Most common PEX; crimp or clamp fittings; slightly stiffer |
| CPVC | 400 | 200°F | 50+ | Hot and cold supply; solvent welded; not for outdoor UV exposure |
| Galvanized Steel | 500 | 300°F | 20-40 | Legacy material; corrodes internally; replacement recommended in older homes |
| Cast Iron (DWV) | gravity/vent only | 300°F | 75-100 | Drain/waste/vent only; excellent sound dampening; very heavy |
| ABS (DWV) | gravity/vent only | 140°F | 50+ | Drain/waste/vent; lightweight; solvent welded; common in western US |
| PVC (DWV) | gravity/vent only | 140°F | 50+ | Drain/waste/vent; most common drain material nationally; solvent welded |