About Vapour Pressure Converter

Vapour pressure is the pressure at which a liquid boils at a given temperature, and it is the term that decides how much of your suction head survives into the NPSH available. Steam tables, Antoine correlations and datasheets all quote it absolute.

Use the absolute column. Vapour pressure is a property measured from a vacuum, not from the atmosphere, so a gauge figure for it is almost always a datasheet that has been filled in loosely. The gauge column is here so a number written that way can still be brought across, and for most liquids at ambient temperature it will come out negative, which is the clue that it was the wrong frame to begin with.

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.