Safe flow capacity at 5 ft/s (Sch 40 PVC)
| Pipe size (Sch 40 PVC ID) | Flow at 5 ft/s | Volume per hour |
|---|---|---|
| 3/4 in | 8.3 GPM | 499 gal/hr |
| 1 in | 13.5 GPM | 808 gal/hr |
| 1-1/4 in | 23.3 GPM | 1,399 gal/hr |
| 1-1/2 in | 31.7 GPM | 1,904 gal/hr |
| 2 in | 52.3 GPM | 3,138 gal/hr |
| 3 in | 113.7 GPM | 6,823 gal/hr |
How to use it
Find your pipe size, read the safe GPM, and keep your zone's total flow (from the Irrigation Flow Calculator) under it. Example: a 1-inch main safely carries about 13.5 GPM - a zone of five 2.5 GPM spray heads (12.5 GPM) just fits; six heads do not.
Why velocity is the limit, not pipe rating
Pipe can physically carry far more than these numbers - but above ~5 ft/s, friction loss climbs steeply and valve slam (water hammer) stresses fittings and sprinklers. Staying under the velocity limit is cheaper than replacing cracked fittings later.
Related tables and tools
- Pressure cost of pushing flow through pipe: see the GPM to PSI Calculator.
- Velocity check for a specific flow: Pipe Flow Calculator.
- Reverse conversion (velocity to GPM): Water Flow Calculator.