Calculate GPM and Velocity for Schedule 40/80 PVC Pipes
Note: Use internal diameter, not nominal size.
Typical range: 2 to 8 ft/s.
Results
Gallons Per Minute (GPM)0.00
Gallons Per Hour (GPH)0.00
Cubic Feet per Second (CFS)0.00
Liters Per Minute (LPM)0.00
Understanding PVC Pipe Flow Rate Calculations
Calculating the flow rate through a PVC pipe is critical for sizing pumps, designing irrigation systems, and residential plumbing. The flow rate depends primarily on the Inside Diameter (ID) of the pipe and the Velocity of the fluid moving through it.
The Mathematical Formula
The calculation uses the continuity equation for fluids:
Q = A × v
Q: Flow Rate
A: Cross-sectional Area of the pipe interior (π × r²)
v: Velocity of the liquid
Schedule 40 vs. Schedule 80 PVC
It is a common mistake to use the nominal pipe size (e.g., 2-inch pipe) as the diameter in the formula. PVC pipes have different wall thicknesses. For example:
Nominal Size
Sch 40 Inside Diameter
Sch 80 Inside Diameter
1″
1.049″
0.957″
2″
2.067″
1.939″
4″
4.026″
3.826″
Recommended Flow Velocities
For most water systems, engineers recommend a velocity between 2 and 5 feet per second (ft/s). Velocities higher than 8 ft/s can cause significant pressure drops, pipe noise, and "water hammer" effects which may damage PVC joints and valves over time.
Example Calculation
If you have a 2-inch Schedule 40 PVC pipe (ID = 2.067 inches) and the water is moving at 5 feet per second: