Impeller Trim Calculator
Flow, head and power after trimming an impeller diameter (affinity approximation).
A trim permanently and cheaply matches an oversized pump to its duty — but unlike a VFD, you can't go back. Keep trims under 75–80% of full diameter.
Formula
Impeller Trim Calculator is a free impeller trim for pump engineers, plumbers and plant designers — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Impeller Trim Calculator
Flow, head and power after trimming an impeller diameter (affinity approximation). The calculation implements Q∝D; H∝D²; P∝D³ (constant speed) (Karassik, Pump Handbook — impeller trimming). A trim permanently and cheaply matches an oversized pump to its duty — but unlike a VFD, you can't go back. Keep trims under 75–80% of full diameter.
How to use Impeller Trim Calculator
- 1Enter Flow at D₁ in m³/h.
- 2Enter Head at D₁ in m.
- 3Enter Power at D₁ in kW.
- 4Enter Full impeller Ø D₁ in mm.
- 5Read New flow, New head, New power instantly — no submit button needed.
- 6Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Impeller Trim Calculator?
- ✓Implements the standard formula — Q∝D; H∝D²; P∝D³ (constant speed)
- ✓Reference cited on-page: Karassik, Pump Handbook — impeller trimming
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Built-in engineering verdict flags out-of-range results instantly
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Impeller Trim Calculator use?+
It computes Q∝D; H∝D²; P∝D³ (constant speed), per Karassik, Pump Handbook — impeller trimming. The formula is displayed under the result.
What should I keep in mind when using this calculator?+
A trim permanently and cheaply matches an oversized pump to its duty — but unlike a VFD, you can't go back. Keep trims under 75–80% of full diameter.
Can I use this for pump selection?+
Use it to establish the duty (flow, head, NPSH, power) and then pick a pump whose curve passes through that point near best efficiency. The tool gives you the engineering numbers a supplier will ask for.
Is the Impeller Trim Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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