Pipe velocity from flow rate
Velocity = flow ÷ cross-sectional area. Enter the flow and the inside diameter of the pipe.
Formulas
v (m/s) = Q (m³/s) / (π d² / 4)v (ft/s) = 0.4085 × Q (gpm) / d² (in²)
Typical design velocities
| Service | ft/s | m/s |
|---|---|---|
| Pump suction lines | 3 to 5 | 0.9 to 1.5 |
| General water, discharge | 5 to 10 | 1.5 to 3 |
| Water mains (buried) | 3 to 7 | 0.9 to 2.1 |
| Hydraulic oil, pressure lines | 15 to 25 | 4.6 to 7.6 |
| Low-velocity air ducts | 8 to 25 (480 to 1,500 fpm) | 2.4 to 7.6 |
Rules of thumb only; check your code and fluid. Erosion, noise and surge limits set the upper end.
Worked example
100 gpm through 2-inch Schedule 40 pipe (2.067 in inside diameter): v = 0.4085 × 100 / 2.067² = 9.56 ft/s (2.91 m/s).