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.