Water Velocity Calculator

Velocity from flow rate and pipe size

Flow velocity equals the volumetric flow rate divided by the cross-sectional area of the pipe. When flow rate is in gallons per minute and pipe diameter is in inches, a unit conversion factor is needed to arrive at velocity in feet per second.

Keeping velocity within recommended ranges prevents pipe erosion, water hammer, and excessive noise. Copper pipe is typically limited to 5 to 8 feet per second, while CPVC and PEX have their own limits specified by the manufacturer.

Noise and erosion limits

Velocities above 5 fps in copper pipe can cause erosion corrosion at elbows and tees. Velocities above 4 fps in residential supply lines can create audible noise in walls. Hot water lines should generally run slower than cold water lines because higher temperatures accelerate erosion.