Pump Affinity Laws Calculator
Apply the pump affinity laws to predict new flow, head and power when a centrifugal pump's speed (RPM) or impeller diameter changes.
Input
Any unit. Fill both diameters to scale for a trimmed or replaced impeller; leave both blank for a speed-only change.
Any flow unit (m³/h, L/s, gpm…) — the result uses the same unit.
Any head unit (m, ft…) — the result uses the same unit.
Any power unit (kW, hp…) — the result uses the same unit.
Output
| Quantity | Current | New | Ratio |
|---|---|---|---|
| No data yet | |||
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/pump-affinity-laws-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"speed1": "1450",
"speed2": "1750",
"flow1": "100",
"head1": "30",
"power1": "12"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `pump-affinity-laws-calculator` tool (Pump Affinity Laws Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
<iframe
src="https://iotools.cloud/embed/pump-affinity-laws-calculator/"
width="100%" height="520" frameborder="0" scrolling="no" loading="lazy"
title="Pump Affinity Laws Calculator — iotools.cloud"
sandbox="allow-scripts allow-forms allow-same-origin allow-downloads allow-popups allow-popups-to-escape-sandbox"
allow="clipboard-write"
style="width:100%;border:1px solid #e5e7eb;border-radius:12px;overflow:hidden"></iframe>
<script src="https://iotools.cloud/embed.js" async></script>Drop this into your own page — free, no key required, just a link back.
| Cost per API/MCP call | From 5 credits |
|---|---|
| Need more credits? | View pricing |
Also available with
Guides
Predict how a centrifugal pump's flow, head and power change when you alter its speed or impeller diameter. Enter the current and new speed (and optionally the impeller diameters), add the operating point you know, and see the scaled values with the ratio applied to each.
The affinity laws
- Flow scales linearly: Q₂ = Q₁ · (N₂/N₁) · (D₂/D₁)
- Head scales with the square: H₂ = H₁ · (N₂/N₁)² · (D₂/D₁)²
- Power scales with the cube: P₂ = P₁ · (N₂/N₁)³ · (D₂/D₁)³
How to use it
- Enter the current and new speed in RPM.
- For an impeller change, fill in both diameters; leave them blank for a speed-only change.
- Enter any of flow, head and power at the current operating point. Units don't matter — results come back in the units you used.
All calculations run in your browser — nothing is uploaded.
How accurate are the affinity laws?
They are exact for speed changes within a modest range and for small impeller trims (roughly under 10–15%). Large diameter changes shift efficiency and the laws become approximate.
Why does a small speed increase cost so much power?
Power rises with the cube of speed, so a 20% speed increase needs about 73% more power, while flow rises only 20%.