How this calculator works
Psig is pressure relative to the surrounding atmosphere. Absolute pressure equals gauge pressure plus ambient pressure. The calculator first establishes absolute pressure, subtracts the selected ambient pressure and converts the difference to psi. A bar is exactly 100,000 Pa. One psi is defined by 0.45359237 kg x 9.80665 m/s2 divided by (0.0254 m)^2, approximately 6,894.757293168 Pa.
Formula
From bara: psig = (bara x 100000 - ambient Pa) / 6894.757293168. From barg: psig = barg x 100000 / 6894.757293168. Reverse: bara = (psig x 6894.757293168 + ambient Pa) / 100000.
Worked example
At 101,325 Pa ambient pressure, 2 bara is approximately 14.3115987705 psig. By contrast, 2 barg is approximately 29.0075475460 psig. Zero psig corresponds to 1.01325 bara at that ambient pressure.
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Frequently asked questions
Why must I choose bara or barg?
Bar identifies a unit but does not identify its zero reference. Confusing absolute and gauge readings introduces an offset equal to ambient pressure.
Can psig be negative?
Yes. A pressure below ambient has a negative gauge reading. It remains valid as long as its absolute pressure is not below zero.
Is the atmospheric offset always 14.7 psi?
No. That is a rounded standard-atmosphere value. Enter local ambient pressure when elevation or weather matters.