Pressure unit converter

Method and scope

All conversions run through kilopascals as the internal reference, using exact or standard-defined factors:

Absolute and gauge

This is the conversion that causes trouble on site, and it is not a unit conversion at all — it is a change of zero point:

• A gauge on the equipment reads gauge pressure. It sits at zero when the enclosure is open to atmosphere, because it is measuring the difference across its own diaphragm.
• Nameplate and standards values are usually absolute. Rated filling pressures in IEC-based documentation are normally quoted as absolute pressure at 20 °C. Confusing the two puts the reading out by about 1 bar — which on a 6 bar system is a 17 % error, comfortably enough to pass a charge that should have failed.
• The suffix is not always there to help. "psig" and "barg" are explicit, but "bar" and "MPa" alone are ambiguous in a lot of supplier documentation. When it matters, confirm which is meant rather than inferring it.
• Altitude changes the relationship. Atmospheric pressure falls roughly 1 kPa per 100 m. At a substation 600 m above sea level the same absolute pressure reads about 0.06 bar higher on a gauge than it would at the coast. Adjust the atmospheric figure above if gauge values matter.

Provided for reference and cross-checking. Does not replace equipment manufacturers' data, nameplate values or operating instructions. Version 1.0.