Enter a pipe's inside diameter and flow rate to calculate the fluid's velocity in ft/s or m/s.
Flow rate alone doesn't say much about what's happening inside a pipe — the same GPM figure crawling through a wide main and racing through a narrow branch line behave completely differently, and velocity is the number that captures that difference.
How to Use the Water Velocity Calculator
Pick US or Metric units, then enter the pipe's inside diameter and its flow rate; velocity updates immediately, shown in both unit systems alongside the pipe's cross-sectional area.
A = π × (diameter ÷ 2)²
V = Q ÷ APlumbing design guidelines commonly keep water velocity in the roughly 2–8 ft/s range for a reason on each end: too slow and sediment settles out inside the pipe instead of getting carried along; too fast and the water itself starts eroding pipe walls and fittings over years of continuous flow, especially at elbows where it changes direction. This calculator doesn't flag either threshold automatically — it just gives the number — but it's worth checking a result against that range before finalizing a pipe size.