Enter the water velocity and diameter of the pipe into the calculator. The calculator will evaluate the volume flow rate of the water moving through the pipe.

Water Flow Rate Calculator

The following equation is used to calculate the volume flow rate of water moving through a pipe given the velocity and pipe diameter.

Q = D^2 * V / .408
  • Where Q is the volume flow rate in gal/min
  • D is the diameter in inches
  • V is the velocity ft/s

To calculate the water flow rate, square the diameter, multiply by the linear velocity, then divide by .408.

Water Flow Rate Definition

Water flow rate is typically either a rate of mass or volume of water that is moving through a pipe. In this case, the equation above solves for gallons per minute.

Water Flow Rate Example

How to calculate water flow rate?

  1. First, determine the diameter of the pipe.

    Measure the diameter of the pipe.

  2. Next, determine the velocity of the flow.

    Measure the water flow velocity.

  3. Finally, calculate the water flow rate.

    Using the formula above, calculate the flow rate in gal/min.


What is water flow?

Water flow is a measure the volume of water moving through an opening per unit of time.

water flow rate calculator
water flow rate formula