Pump Sizing 101: Flow, Head, and NPSH Explained

Sizing a pump comes down to matching the pump's performance curve to your system. Get three numbers right and the rest of the selection falls into place: flow rate, total head, and NPSH available.

Flow rate is how much fluid you need to move, usually in gallons per minute (GPM). Base it on real demand — peak, average, and minimum — rather than a single worst-case guess, because oversizing wastes energy and causes a pump to run off its best-efficiency point.

Total dynamic head (TDH) is the resistance the pump must overcome, expressed in feet. It combines static lift (the vertical distance), friction losses in the pipe and fittings, and any pressure you need at the outlet. Long runs, small pipe, and lots of elbows all add friction head quickly.

NPSH — net positive suction head — is the margin that keeps a pump from cavitating. Compare the NPSH available in your system to the NPSH required by the pump at your operating point, and keep a comfortable buffer. Hot fluids, high elevation, and long suction lines all reduce NPSH available.

With flow, head, and NPSH in hand, a performance curve tells the whole story. If you send us those numbers with your fluid and temperature, we can shortlist pumps that land near their best-efficiency point instead of the edges of the curve.