About Pressure Converter

Absolute pressure is measured from a perfect vacuum; gauge pressure is measured from whatever the atmosphere is doing around the instrument. A gauge reading of zero and an absolute reading of zero are not the same pressure, which is why every unit here is labelled with the frame it belongs to.

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.