Convert PSIG To PSIA: Calculator + Conversion Chart (Dead Simple)

How to convert PSIG to PSIA? In HVAC, we mostly deal with PSIG (gauge pressure). All refrigerant pressure temperature charts, for example, include PSIG instead of PSIA. For everybody who needs to convert PSIG to PSIA (absolute pressure), we have created a simple PSIG to PSIA calculator (insert PSIG, get PSIA) as well as a conversion chart for 0 PSIG to 1000 PSIG converted to PSIA.

Namely, the difference between PSIG and PSIA is that PSIG is a relative unit and PSIA is an absolute unit. Here is a short summary of both of these pressure units:

  • PSIG or Pound per Square Inch Gauge is the pressure we measure with an HVAC gauge. This gauge pressure is measured not relative to vacuum like PSIA but relative to atmospheric pressure. If we were to use an HVAC gauge and measure the pressure at sea levels, we would get that the pressure is equal to 0.0 PSIG.
  • PSIA or Pound per Square Inch Absolute is the absolute pressure (measured relative to vacuum). It does not account for the atmospheric pressure like PSIG. At sea level, the absolute pressure is equal to 14.7 PSIA.

It’s very easy to convert PSIG to PSIA. You just need to use this PSIG to PSIA conversion formula:

PSIA = PSIG + 1 atm = PSIG + 14.7 PSI

In short, to calculate PSIA from PSIG, you need to add 1 atmospheric pressure to PSIG. At sea level, this atmospheric pressure is equal to 14.7 PSI; that’s why we add 14.7 PSI. At higher elevations, the atmospheric pressure is lower.

Example: Let’s say that your HVAC gauge reads 100 PSIG. How many PSIA is that? We just use the equation above:

100 PSIG + 14.7 PSI = 114.7 PSIA

At 100 PSIG, the absolute pressure is equal to 114.7 PSIA.

Note about wrong conversions: 1 PSIG is equal to 15.7 PSIA. That doesn’t mean that 2 PSIG is equal to 31.4 PSIA because this is not a linear relationship; it is a relationship by addition.

You can calculate PSIA from PSIG using a pocket calculator but that can be a bit tedious. The simpler way is to use the following PSIG to PSIA calculator or consult the conversion chart you will find below the calculator:

PSIG To PSIA Calculator


It’s rather easy to use this calculator.

Let’s say that your gauge tells you the refrigerant you are measuring has a 120 PSIG pressure. What is absolute pressure (PSIA)? Just insert ‘120’ in the calculator above and you get the result: 120 PSIG is equal to 134.7 PSIA.

Here is the promised conversion chart:

PSIG To PSIA Conversion Table

PSIG (Gauge Pressure): PSIA (Absolute Pressure):
0 PSIG 14.7 PSIA
5 PSIG 19.7 PSIA
10 PSIG 24.7 PSIA
15 PSIG 29.7 PSIA
20 PSIG 34.7 PSIA
25 PSIG 39.7 PSIA
30 PSIG 44.7 PSIA
40 PSIG 54.7 PSIA
50 PSIG 64.7 PSIA
60 PSIG 74.7 PSIA
70 PSIG 84.7 PSIA
80 PSIG 94.7 PSIA
90 PSIG 104.7 PSIA
100 PSIG 114.7 PSIA
110 PSIG 124.7 PSIA
120 PSIG 134.7 PSIA
130 PSIG 144.7 PSIA
140 PSIG 154.7 PSIA
150 PSIG 164.7 PSIA
160 PSIG 174.7 PSIA
170 PSIG 184.7 PSIA
180 PSIG 194.7 PSIA
190 PSIG 204.7 PSIA
200 PSIG 214.7 PSIA
250 PSIG 264.7 PSIA
300 PSIG 314.7 PSIA
350 PSIG 364.7 PSIA
400 PSIG 414.7 PSIA
450 PSIG 464.7 PSIA
500 PSIG 514.7 PSIA
600 PSIG 614.7 PSIA
700 PSIG 714.7 PSIA
800 PSIG 814.7 PSIA
900 PSIG 914.7 PSIA
1000 PSIG 1014.7 PSIA

Hopefully, now you have a good understanding of the difference between PSIG and PSIA, and how to easily convert one into the other. If you need any help, you can always use the comments below and we will help you out.

You can also check out a similar calculator for PSIA to PSIG conversion here.

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