Pipe Flow Velocity Calculator (Liquid)
- Sullair dealer since 1984
- Serving industry since 1978
- No form fill, nothing gated
What this calculator tells you
Pipe size problems hide until the pump starts complaining. Check your line velocity against suction and discharge guidelines in seconds.
Your Line
Results
Velocity in the line:
0 ft/s
Undersized suction piping is one of the most common causes of pump failure we see in the field.
How this is calculated
- Velocity (ft/s) = 0.408 x GPM / d², where d is the pipe's true inner diameter in inches (schedule 40 steel IDs, not nominal sizes).
- Guidelines: pump suction lines 2 to 4 ft/s (amber to 6, red above), discharge and general service 5 to 10 ft/s (amber to 12, red above).
- When the velocity is out of range, the recommendation is the smallest listed pipe size whose velocity lands inside the green band at your flow.
Estimates only. Actual results depend on your equipment and operating conditions. Call 800.825.3222 for exact sizing.
Common questions
What is a good liquid velocity in pump piping?
Common guidelines are 2 to 4 feet per second in pump suction lines and 5 to 10 feet per second in discharge and general service lines. Suction lines run slower on purpose: every foot of extra velocity costs suction pressure right where the pump can least afford it.
How do I calculate velocity in a pipe from GPM?
Velocity in feet per second = 0.408 x GPM / d squared, where d is the pipe's true inner diameter in inches. Use the actual inner diameter, not the nominal size: a 2 inch schedule 40 steel pipe is really 2.067 inches inside, and the difference matters at higher flows.
What happens if pipe velocity is too high?
On the suction side, high velocity eats the pressure margin that keeps the liquid from flashing to vapor, which invites cavitation. On the discharge side, velocities much above 10 to 12 feet per second accelerate erosion, raise friction losses sharply, and make water hammer worse when valves close. Going one pipe size up is usually cheap insurance.
Want a tech to verify these numbers at your facility?
Request received. If you need someone now, call 800.825.3222.
Please fill in all required fields (name, company, email, phone, preferred contact method, ZIP, and city), or call 800.825.3222.
These are estimates. Your pump curve has the real answer.
Our pump team checks flow, head, and NPSH against the manufacturer curve before anything is quoted. Since 1978, across 14 Midwest locations.