Friction loss per 100 ft (PSI, PVC C=150)
| Pipe size (Sch 40 PVC ID) | 5 GPM | 10 GPM | 15 GPM | 20 GPM | 25 GPM |
|---|---|---|---|---|---|
| 3/4 in (0.824") | 0.9 | 3.4 | 7.1 | 12.1 | 18.3 |
| 1 in (1.049") | 0.3 | 1.0 | 2.2 | 3.7 | 5.6 |
| 1-1/4 in (1.380") | 0.1 | 0.3 | 0.6 | 1.0 | 1.5 |
| 1-1/2 in (1.610") | 0.0 | 0.1 | 0.3 | 0.5 | 0.7 |
| 2 in (2.067") | 0.0 | 0.0 | 0.1 | 0.1 | 0.2 |
Reading the table
- Small pipe punishes flow. 25 GPM in 3/4-inch pipe burns ~17 PSI per 100 ft; in 1-inch pipe the same flow costs ~6 PSI - and in 2-inch pipe it is almost free.
- Length multiplies everything. A 200 ft run doubles the listed loss; 300 ft triples it.
- Fittings add more. Each elbow or valve behaves like extra pipe length - a common allowance is 10-20% on top of measured runs.
How to use it in a design
Add up your worst-case path: meter to farthest head. Keep total losses (pipe + fittings + elevation: 1 PSI per 2.31 ft of rise) small enough that the head still gets its required working pressure from your static pressure. If the math does not fit, upsize one pipe size - it is the cheapest fix available.
For a quick single-point conversion, use the GPM to PSI Calculator; for velocity checks, the Pipe Flow Calculator.