Pump Sizing Calculator: Flow, Total Head, and Horsepower
- Sullair dealer since 1984
- Serving industry since 1978
- No form fill, nothing gated
What this calculator tells you
Enter your flow, lift, piping, and discharge pressure to get total dynamic head, brake horsepower, and a recommended motor size.
Your System
Results
Total dynamic head:
0 feet
Brake horsepower: 0 HP
Recommended motor: 0 HP (next standard size above brake HP with a 15% margin)
Friction head from piping: 0 feet
We size Grundfos, Paco, and Peerless pumps against your real system curve. Send us these numbers and we will confirm the selection. Pump Team: 920-393-4958 ext 2401.
How this is calculated
- Friction head (Hazen-Williams): hf = 0.2083 x (100/C)^1.85 x Q^1.85 / d^4.8655 x L/100, with Q in GPM, d in inches, L in feet, and C the material roughness coefficient (steel 120, PVC 150, old steel 90).
- TDH (feet) = static lift + discharge elevation + friction head + (discharge PSI x 2.31 / specific gravity).
- Brake HP = GPM x TDH x specific gravity / (3,960 x pump efficiency).
- Recommended motor = brake HP x 1.15, rounded up to the next standard motor size.
Estimates only. Actual results depend on your equipment and operating conditions. Call 800.825.3222 for exact sizing.
Common questions
How do I calculate total dynamic head for a pump?
Total dynamic head (TDH) is the sum of static suction lift, discharge elevation, friction losses through the piping, and any pressure required at the discharge converted to feet (PSI x 2.31 divided by specific gravity). Friction losses are commonly estimated with the Hazen-Williams formula, which depends on flow rate, pipe diameter, pipe length, and the pipe material's roughness coefficient.
How much horsepower does a pump need?
Brake horsepower = GPM x TDH x specific gravity / (3,960 x pump efficiency). A pump moving 100 GPM against 55 feet of head at 65 percent efficiency needs about 2.1 brake HP. Motors are then selected one standard size above brake HP with margin, so the motor is not overloaded anywhere on the pump curve.
What is a typical pump efficiency to assume?
Small to mid size centrifugal pumps typically run 55 to 75 percent efficient at their best efficiency point, so 65 percent is a reasonable planning assumption. Actual efficiency depends on the specific pump model and where your duty point falls on its curve, which is why the final selection should be checked against the manufacturer's curve.
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.