About Suction Pressure Converter

Suction pressure is read at the pump inlet, and the frame of reference decides what the number means. A suction gauge reads gauge pressure, but NPSH available is an absolute calculation, so a reading taken off the gauge has to be moved to the absolute frame before it goes anywhere near a cavitation margin.

Suction pressure below atmospheric is negative in gauge and still positive in absolute, which is the single most common place this conversion gets skipped.

Gauge and absolute differ by one standard atmosphere, 101325 Pa exactly. Every offset on this page is derived from that one constant, so the same reading converts to the same pressure whichever unit you ask for.