Do these laws include efficiency changes?

They assume comparable operating points. Real pumps deviate with speed; use manufacturer data for final selection.

Can I use this for fans?

The same proportionalities are often used for incompressible fan scaling at moderate pressure changes, but compressibility matters for large pressure swings.

Pump Affinity Laws Calculator

Affinity laws for the same impeller at two speeds: flow scales with speed ratio, head with the square, and power with the cube, for incompressible pump scaling at comparable efficiency assumptions. Use for preliminary what-if speed changes, not as a substitute for manufacturer curves.

Free · No limits · Runs in your browser

How to use

1Enter reference speed and the new operating speed (same units on both, e.g. rpm).
2Enter reference flow, head, and shaft power at the reference speed.
3Read scaled flow, head, and power at the new speed using the same units you provided.

Frequently asked questions

Do these laws include efficiency changes?: They assume comparable operating points. Real pumps deviate with speed; use manufacturer data for final selection.
Can I use this for fans?: The same proportionalities are often used for incompressible fan scaling at moderate pressure changes, but compressibility matters for large pressure swings.