NPSH Available Calculator
Calculate net positive suction head available (NPSHa) for a pump system from source pressure, vapor pressure, specific gravity, static suction head and suction-line friction loss.
Input
SI metric enters pressures in kPa and heads in metres; US customary uses psi and feet.
Absolute pressure at the liquid's free surface — atmospheric pressure for an open tank (101.325 kPa / 14.7 psi at sea level), or tank gauge pressure plus atmospheric for a closed/pressurized tank.
Absolute vapor pressure of the pumped liquid at its operating temperature (e.g. water at 20°C is about 2.339 kPa / 0.339 psi).
Specific gravity of the pumped liquid relative to water (water = 1.0).
Elevation of the liquid source relative to the pump centerline. Positive for a flooded suction (source above the pump), negative for a suction lift (source below).
Total friction and minor-loss head in the suction piping (pipe friction plus fittings, strainer, foot valve, etc.).
Output
| Metric | Value |
|---|---|
| No data yet | |
One-line NPSH available result.
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/npsh-available-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"unitSystem": "si",
"atmosphericPressure": "101.325",
"vaporPressure": "2.339",
"specificGravity": "1.0",
"staticSuctionHead": "2",
"frictionLossSuction": "1.2"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `npsh-available-calculator` tool (NPSH Available 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/npsh-available-calculator/"
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title="NPSH Available Calculator — iotools.cloud"
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allow="clipboard-write"
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<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 |
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Guides
The NPSH Available Calculator computes Net Positive Suction Head Available (NPSHa) — the margin above a liquid's vapor pressure that a pump's suction side actually has once source pressure, elevation and suction-line friction losses are accounted for. A pump cavitates once NPSHa drops below the manufacturer's rated NPSH required (NPSHr), so checking this margin is a core step in pump selection and troubleshooting.
How to use it
- Pick your unit system — SI metric (kPa, m) or US customary (psi, ft).
- Enter the source pressure — atmospheric pressure for an open tank, or tank gauge pressure plus atmospheric for a closed/pressurized tank.
- Enter the liquid's vapor pressure at its operating temperature.
- Enter the liquid's specific gravity relative to water.
- Enter the static suction head — positive for a flooded suction (the source sits above the pump centerline), negative for a suction lift (the source sits below).
- Enter the suction-line friction loss — total friction and minor losses (pipe, fittings, strainer, foot valve) between the source and the pump inlet.
Results update instantly: the source pressure head and vapor pressure head (both converted from pressure via the liquid's specific gravity), the static suction head and friction loss carried through, and the resulting NPSH available. A one-line summary flags whether the margin is positive or at cavitation risk.
The formula
NPSHa = Ha + Hs − Hf − Hvpwhere Ha is the absolute pressure head at the liquid's free surface, Hs is the static suction head (signed), Hf is the suction-line friction head loss, and Hvp is the liquid's vapor-pressure head. Pressure converts to head via the liquid's specific gravity: h(m) = P(kPa) / (9.80665 × SG) in SI, or h(ft) = P(psi) × 144 / (62.4 × SG) in US customary.
A pump needs NPSHa to exceed its rated NPSH required (NPSHr, from the pump curve) by a comfortable margin — commonly at least 0.5–1 m (2–3 ft) — to avoid cavitation, noise, vibration and impeller damage.
Is my data private?
Completely. Every calculation runs entirely in your browser. Nothing you type is uploaded, stored or sent to a server.