Pipe Flow Rate Calculator
Enter a pipe diameter and either the flow velocity or the flow rate. The calculator finds the missing value and the cross-sectional area, then converts to L/min and GPM.
How to calculate pipe flow rate
- Enter the inside pipe diameter in metres.
- Enter either the flow velocity or the volumetric flow rate.
- Read the missing value plus the area, litres per minute and gallons per minute.
Examples
Flow rate from velocity
diameter = 0.1 m, velocity = 3 m/s
Q = 0.023562 m3/s (1413.72 L/min, 373.46 GPM)
Velocity from flow rate
diameter = 0.1 m, flow rate = 0.023562 m3/s
velocity = 3 m/s
Frequently asked questions
What is the pipe flow rate formula?
Flow rate Q equals area times velocity, Q = A x v. For a round pipe the area is A = pi x (D / 2) squared, where D is the inside diameter.
What units does the calculator use?
Inputs are SI: metres for diameter, metres per second for velocity, cubic metres per second for flow rate. Output also shows L/min and US GPM.
How do I convert m3/s to GPM?
Multiply cubic metres per second by 15850.323 to get US gallons per minute, or by 60000 to get litres per minute.
Does this use inside or outside diameter?
Use the inside diameter of the pipe. The fluid only fills the bore, so the outside diameter would overstate the area and the flow rate.
Why must the diameter be greater than zero?
The area depends on the diameter squared, and a zero diameter gives zero area, which would make the velocity calculation divide by zero.
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