PSIG to PSIA Converter
Unit ConversionConvert a gauge pressure in psig to absolute pressure in psia by adding the standard atmosphere, about 14.6959 psi, down to a full vacuum.
PSIA (absolute)
Equivalent absolute pressure, assuming standard sea-level atmosphere
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SponsoredThis converter turns a gauge pressure in psig into absolute pressure in psia. Enter a gauge reading and the result updates as you type. It adds the standard atmosphere, about 14.6959 psi, to the reading.
PSIG (gauge) is what a tire, tank or compressor gauge reads: it is zeroed against the surrounding air, so it shows 0 at normal air pressure. PSIA (absolute) is measured from a perfect vacuum. The two differ by the air pressure around the gauge, which this converter takes as the standard atmosphere, about 14.6959 psi.
Gauge readings below the surrounding air are negative, so negative values are accepted down to a full vacuum, about -14.6959 psig. Below that the result shows a dash, because no pressure is lower than a perfect vacuum. The result is rounded to 4 decimal places.
How to Convert PSIG to PSIA
To convert psig to psia, add the air pressure around the gauge: psia = psig + 14.6959 at the standard atmosphere. To go back from psia to psig, subtract the same amount.
For example, 30 psig is about 44.6959 psia, and 0 psig, a gauge reading at normal air pressure, is about 14.6959 psia.
PSIG to PSIA Conversion Table
Common gauge values converted to absolute pressure, rounded to 4 decimal places.
| PSIG | PSIA |
|---|---|
| -14 psig | 0.6959 psia |
| -10 psig | 4.6959 psia |
| -5 psig | 9.6959 psia |
| 0 psig | 14.6959 psia |
| 15 psig | 29.6959 psia |
| 30 psig | 44.6959 psia |
| 50 psig | 64.6959 psia |
| 100 psig | 114.6959 psia |
| 150 psig | 164.6959 psia |
| 500 psig | 514.6959 psia |
Local Air Pressure vs the Standard Atmosphere
The 14.6959 psi added here is the standard atmosphere, 101,325 Pa. Real air pressure is lower at higher elevation and rises and falls with the weather, as NOAA explains, so the true offset at your gauge is often different. For careful work, add the local barometric pressure instead, converted to psi with the Barometric Pressure Converter listed below.
Air Pressure at Altitude
Standard air pressure at different elevations, from the pressure altitude formula in the National Weather Service calculator notes, rounded. At 5,000 ft you would add about 12.23 psi, not 14.7.
| Elevation (ft) | Air Pressure (psi) | Air Pressure (kPa) |
|---|---|---|
| 0 ft | 14.7 psi | 101.3 kPa |
| 1,000 ft | 14.17 psi | 97.7 kPa |
| 2,000 ft | 13.66 psi | 94.2 kPa |
| 3,000 ft | 13.17 psi | 90.8 kPa |
| 5,000 ft | 12.23 psi | 84.3 kPa |
| 7,500 ft | 11.12 psi | 76.7 kPa |
| 10,000 ft | 10.1 psi | 69.7 kPa |
Forgetting the air pressure is a bigger error than it looks: a system at 100 psig is about 114.7 psia, so using 100 in a gas-law calculation understates the absolute pressure by about 12.8%. Writing psig or psia, never plain psi, keeps the two apart.
Gas law calculations, such as those in the Ideal Gas Law Calculator, need absolute pressure. Air pressure also drops with altitude, which the Oxygen Saturation Altitude Estimator relates to blood oxygen.
Frequently Asked Questions
Does temperature or altitude change psig to psia?
Temperature does not enter the conversion. Altitude and weather do, because they change the air pressure you add: standard air pressure is about 12.23 psi at 5,000 ft, not 14.7.
What is 0 psig in psia?
0 psig means the pressure equals the surrounding air, so it is about 14.6959 psia at the standard atmosphere, or about 12.23 psia at 5,000 ft.
How do I convert psia to psig?
Subtract the air pressure around the gauge, about 14.6959 psi at the standard atmosphere. A result below zero means the pressure is below the surrounding air, a partial vacuum.
Is converting psig to psia a unit change?
No. Both use the same unit, the psi; they only measure from different zero points. That is why the conversion adds or subtracts a pressure instead of multiplying by a factor.
Can I enter a negative value?
Yes. A negative gauge reading is a partial vacuum. The lowest possible value is a full vacuum, about -14.6959 psig at standard air pressure, so lower values show a dash instead of a result.
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