PSIG to PSIA Converter
Convert gauge pressure to absolute pressure, or work backward from PSIA to PSIG, using a 14.7 psi standard sea-level atmospheric reference.
Pressure input
Enter gauge pressure at or above – 14.70 PSIG. U.S. decimal notation and properly grouped thousands are accepted.
Enter absolute pressure at or above 0 PSIA. Editing this field calculates the equivalent gauge pressure.
Live result
30.00 PSIG plus 14.70 psi atmospheric reference equals 44.70 PSIA.
Conversion breakdown
| Component | Value | Meaning |
|---|---|---|
| Gauge pressure | 30.00 PSIG | Pressure relative to the selected atmospheric reference. |
| Atmospheric reference | 14.70 psi | Standard sea-level offset used by this conversion. |
| Absolute pressure | 44.70 PSIA | Pressure measured from a perfect-vacuum zero. |
How to use this PSIG to PSIA converter
What this calculator does
This calculator converts between gauge pressure, expressed as PSIG, and absolute pressure, expressed as PSIA. Gauge pressure is referenced to the surrounding atmosphere, while absolute pressure is referenced to a perfect vacuum. The conversion used here is the standard practical relationship PSIA = PSIG + 14.7, with 14.7 psi treated as a sea-level atmospheric reference. That makes the tool useful for quick engineering checks, equipment documentation, training examples, and pressure-data reconciliation when a specification uses one pressure basis and an instrument uses the other. It does not estimate the actual local barometric pressure at your site, so it should not be used as a substitute for a measured atmospheric-pressure correction when elevation or weather must be modeled precisely.
The NIST pressure conversion table confirms the relationship between psi and SI pressure units, while the National Weather Service explains why atmospheric pressure changes with the weight of the air above a location.
When to use it
- Translate a pressure-gauge reading in PSIG into the absolute pressure needed for a thermodynamic or process calculation.
- Work backward from a datasheet value in PSIA to the gauge pressure an operator would expect to see.
- Check whether two specifications differ only because one uses gauge pressure and the other uses absolute pressure.
- Build a quick, reproducible pressure-conversion record in Excel for a calculation package or engineering note.
How to calculate
- The calculator opens with a complete demonstration: 30 PSIG and its corresponding 44.70 PSIA. The example workbook is already validated in the browser, so Download Excel is available immediately.
- To convert gauge to absolute pressure, replace the value in Pressure in pounds per square inch gauge. The PSIA field, result cards, breakdown table, live summary, and workbook data update from the same calculation model.
- To convert in the opposite direction, edit Pressure in pounds per square inch absolute. The converter subtracts 14.7 psi and updates the PSIG value.
- Review the large Absolute pressure result first, then use Gauge equivalent, Atmospheric reference, and PSIA – PSIG as cross-checks. The three-row Conversion breakdown shows the same identity in table form.
- Select Download Excel to export the current validated values as a real .xlsx workbook. Select Reset to clear the demonstration and all calculated output. Reset intentionally leaves the fields empty and may disable Excel export until you enter a complete valid value again.
Input guide
Pressure in pounds per square inch gauge accepts a required decimal pressure in PSIG when you choose to enter the gauge side. Plain U.S. decimals such as 30, 30.5, or – 5 are accepted, as are correctly grouped values such as 1,250.25. Scientific notation and decimal-comma forms such as 1,5 are rejected rather than silently reinterpreted. The supported domain begins at – 14.70 PSIG, because a lower gauge value would imply a negative absolute pressure under this model. A realistic example is 30 PSIG. Raising PSIG raises PSIA one-for-one. A common mistake is assuming a gauge reading already includes atmospheric pressure.
Pressure in pounds per square inch absolute accepts a required decimal pressure in PSIA when you enter the absolute side. Its minimum is 0 PSIA, representing the ideal absolute-pressure floor. A realistic example is 44.70 PSIA. Raising PSIA raises the equivalent PSIG one-for-one. Do not enter a negative absolute pressure; if you need to represent pressure below ambient, enter a negative gauge pressure instead, provided it remains at or above – 14.70 PSIG.
Output guide
Absolute pressure is the primary result in PSIA. It is an exact arithmetic conversion within the stated 14.7 psi assumption, not a forecast or recommendation. Gauge equivalent is the corresponding PSIG value and can be negative when absolute pressure lies between 0 and 14.7 PSIA. Atmospheric reference shows the fixed 14.70 psi offset used by this calculator. PSIA – PSIG is a consistency check and should remain 14.70 psi for every valid state. The three live pills repeat gauge pressure, absolute pressure, and the fixed offset for quick scanning. In the Conversion breakdown, the Component column names the term, Value shows its current pressure, and Meaning describes its role in the identity.
Worked example
With the startup value of 30 PSIG, add the 14.7 psi atmospheric reference: 30 + 14.7 = 44.7. The first-open result therefore displays 44.70 PSIA. Reversing the same example gives 44.7 – 14.7 = 30, so the gauge equivalent returns to 30.00 PSIG. This direct offset is why the displayed difference remains 14.70 psi at every valid pressure.
Why the atmospheric reference matters
PSIG and PSIA describe the same physical dimension but use different zero references. A typical gauge is zeroed against ambient air, so 0 PSIG means the measured pressure equals the surrounding atmospheric pressure. PSIA instead uses a vacuum as zero. Under the standard approximation used here, 0 PSIG corresponds to 14.70 PSIA, and – 14.70 PSIG corresponds to 0 PSIA.
The 14.7 psi offset is a standard sea-level approximation rather than a universal local constant. The National Weather Service pressure explainer notes that average sea-level atmospheric pressure is about 14.7 psi and that atmospheric pressure changes as the amount of air above a surface changes. For higher-precision work, use the actual local absolute atmospheric pressure as required by your method or instrumentation rather than assuming sea-level conditions.
Pressure units and cross-checking
If your workflow also uses pascals or kilopascals, NIST lists 1 psi as approximately 6,894.757 Pa in its SI conversion factors for pound-force per square inch. Keeping the pressure basis and the pressure unit separate helps prevent two common errors: converting units correctly but using the wrong gauge/absolute reference, or using the correct reference while mixing psi with kPa or another unit.