GPM to PSI Calculator
Calculate pressure loss from flow rate using the Hazen-Williams formula. Perfect for plumbing, irrigation, fire protection, and hydraulic system design.
Calculate friction head loss in pipes based on flow rate, pipe diameter, length, and material. Uses industry-standard Hazen-Williams equation.
GPM to PSI Converter
Water flow rate through the pipe
Inner diameter of the pipe
Total length of pipe run
Higher C = smoother pipe = less friction loss
Advanced Parameters
+ for up, - for down
Calculation Results
Enter flow rate and pipe details
then click "Calculate" for pressure loss
GPM to PSI Calculator
Understanding the relationship between flow rate (GPM) and pressure loss (PSI) is crucial for designing efficient water systems. This calculator uses the Hazen-Williams formula, the industry standard for calculating friction head loss in pipes.
The Hazen-Williams Formula
The Hazen-Williams equation is the most widely used formula for calculating pressure loss in water systems:
C = Hazen-Williams coefficient (pipe roughness)
d = Pipe inner diameter (inches)
L = Pipe length (feet)
Flow = 50 GPM, Pipe = 2 inch, Length = 100 ft, C = 120 (Steel)
PSI = (4.52 × 501.85) ÷ (1201.85 × 24.87) × 100
PSI = 3.24 PSI
Hazen-Williams C Values
The C coefficient represents pipe smoothness. Higher values mean smoother pipes with less friction:
| Pipe Material | C Value | Condition |
|---|---|---|
| PVC/Plastic | 150 | Very smooth |
| HDPE | 140 | Smooth |
| Copper | 130 | Smooth |
| Steel | 120 | New |
| Steel | 110 | 15 years old |
| Cast Iron | 100 | Average |
| Cast Iron | 90 | Old/rusted |
| Galvanized Iron | 80 | Rough |
GPM to PSI Reference Table
Here's a comprehensive reference table showing pressure loss for various flow rates and pipe sizes (100 ft length, Steel pipe C=120):
| Flow (GPM) | Pipe Dia (in) | Velocity (ft/s) | Pressure Loss (PSI) | Loss (ft Head) |
|---|---|---|---|---|
| 10 GPM | 1" | 3.7 | 3.2 PSI | 7.4 ft |
| 20 GPM | 1.5" | 3.6 | 2.8 PSI | 6.5 ft |
| 30 GPM | 2" | 3.1 | 1.4 PSI | 3.2 ft |
| 50 GPM | 2" | 5.1 | 3.2 PSI | 7.4 ft |
| 75 GPM | 2.5" | 4.9 | 2.5 PSI | 5.8 ft |
| 100 GPM | 3" | 4.4 | 1.6 PSI | 3.7 ft |
| 150 GPM | 3" | 6.6 | 3.4 PSI | 7.9 ft |
| 200 GPM | 4" | 5.1 | 1.5 PSI | 3.5 ft |
| 250 GPM | 4" | 6.4 | 2.2 PSI | 5.1 ft |
| 300 GPM | 4" | 7.7 | 3.1 PSI | 7.2 ft |
| 400 GPM | 6" | 4.5 | 0.8 PSI | 1.9 ft |
| 500 GPM | 6" | 5.7 | 1.2 PSI | 2.8 ft |
| 750 GPM | 8" | 4.8 | 0.5 PSI | 1.2 ft |
| 1000 GPM | 8" | 6.4 | 0.9 PSI | 2.1 ft |
| 1500 GPM | 10" | 6.1 | 0.6 PSI | 1.4 ft |
| 2000 GPM | 10" | 8.2 | 1.0 PSI | 2.3 ft |
| 2500 GPM | 12" | 7.1 | 0.6 PSI | 1.4 ft |
| 3000 GPM | 12" | 8.5 | 0.8 PSI | 1.9 ft |
| 5000 GPM | 16" | 8.0 | 0.5 PSI | 1.2 ft |
| 10000 GPM | 24" | 7.1 | 0.3 PSI | 0.7 ft |
For efficient water system design, keep flow velocity between 3-7 ft/s. Velocities below 3 ft/s may allow sediment buildup, while velocities above 7 ft/s cause excessive pressure loss, noise, and pipe erosion. Use larger pipes for higher flow rates to maintain optimal velocity.