NPSH Available Calculator

About this calculator

NPSHa (Net Positive Suction Head available) tells you how much pressure margin exists at a pump’s suction inlet above the fluid’s vapor pressure. It’s derived from atmospheric pressure and vapor pressure, converted to head, plus the static head of the fluid at the source, minus friction losses in the suction piping: roughly NPSHa = (Patm − Pvapor)/(ρg) + hs − hf.

Pump engineers compare NPSHa against the pump manufacturer’s required value, NPSHr: if available head falls below required head, the fluid flashes to vapor inside the pump and causes cavitation — a condition that erodes impellers, causes noise and vibration, and can wreck a pump over time. This calculator is a standard part of the workflow for mechanical and process engineers sizing pumps and laying out suction piping in industrial and municipal water systems.