Water Velocity Calculator
Calculate water velocity in pipes from flow rate and diameter to check for noise and erosion limits.
Results
Visualization
How It Works
Water velocity in pipes should be kept between 2-8 ft/s. Too fast causes noise, erosion, and water hammer. Too slow causes sediment buildup and stagnation.
The Formula
V = 0.4085 x GPM / D^2 (where D is in inches)
Variables
- V — Velocity in feet per second
- GPM — Flow rate in gallons per minute
- D — Inside diameter in inches
Worked Example
For 10 GPM through a 3/4" pipe: V = 0.4085 x 10 / 0.75^2 = 7.26 ft/s. This is near the upper limit.
Practical Tips
- Maximum 8 ft/s for copper to prevent erosion
- Maximum 5 ft/s recommended for residential to reduce noise
- Hot water recirculation should be 2-4 ft/s
- Water hammer is worse at higher velocities