Pump Affinity Laws Calculator
New flow, head and power when pump speed changes — the VFD designer's first tool.
The cube law is why VFDs pay for themselves: 76% speed = 44% power. Caveat: real savings depend on the system curve having low static head.
Formula
Pump Affinity Laws Calculator is a free affinity laws 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 Pump Affinity Laws Calculator
New flow, head and power when pump speed changes — the VFD designer's first tool. The calculation implements Q∝N; H∝N²; P∝N³ (ANSI/HI 14.3 — affinity rules). The cube law is why VFDs pay for themselves: 76% speed = 44% power. Caveat: real savings depend on the system curve having low static head.
How to use Pump Affinity Laws Calculator
- 1Enter Flow at N₁ in m³/h.
- 2Enter Head at N₁ in m.
- 3Enter Power at N₁ in kW.
- 4Enter Original speed N₁ in rpm.
- 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 Pump Affinity Laws Calculator?
- ✓Implements the standard formula — Q∝N; H∝N²; P∝N³
- ✓Reference cited on-page: ANSI/HI 14.3 — affinity rules
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Live worked example: the substitution recomputes from your numbers
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Pump Affinity Laws Calculator use?+
It computes Q∝N; H∝N²; P∝N³, per ANSI/HI 14.3 — affinity rules. The formula is displayed under the result along with a worked example substituted with your own inputs.
What should I keep in mind when using this calculator?+
The cube law is why VFDs pay for themselves: 76% speed = 44% power. Caveat: real savings depend on the system curve having low static head.
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 Pump Affinity Laws 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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