Absolute to Gauge Pressure Calculator (and Vacuum)
By Santaji GadepatilinUpdated November 5, 2026
Gauge pressure is measured relative to the surrounding atmosphere, absolute pressure relative to a perfect vacuum, and the difference is the local atmospheric pressure. This absolute to gauge pressure calculator converts between them — and handles vacuum as negative gauge pressure — as explained in absolute vs gauge pressure and how to calculate vacuum pressure.
How to use the absolute to gauge pressure calculator
Enter the gauge pressure (use a negative value for vacuum) and the altitude. The calculator estimates atmospheric pressure with the standard-atmosphere formula and returns the absolute pressure. To convert absolute to gauge, clear the gauge pressure and enter the absolute value. If you have a barometer reading, clear the altitude and enter the atmospheric pressure directly.
Absolute pressure formulas
pabs = pgauge + patm · patm = 101,325 × (1 − 2.25577×10⁻⁵ z)5.25588 Pa
Worked example
2 bar(g) at sea level:
- patm = 1.01325 bar
- pabs = 2 + 1.01325 = 3.01325 bar(a)
Standard atmospheric pressure by altitude
| Altitude | kPa | bar | psi |
|---|---|---|---|
| 0 m | 101.33 kPa | 1.0132 bar | 14.70 psi |
| 500 m | 95.46 kPa | 0.9546 bar | 13.85 psi |
| 1,000 m | 89.87 kPa | 0.8987 bar | 13.04 psi |
| 1,500 m | 84.56 kPa | 0.8456 bar | 12.26 psi |
| 2,000 m | 79.50 kPa | 0.7950 bar | 11.53 psi |
| 3,000 m | 70.11 kPa | 0.7011 bar | 10.17 psi |
| 4,000 m | 61.64 kPa | 0.6164 bar | 8.94 psi |
| 5,000 m | 54.02 kPa | 0.5402 bar | 7.83 psi |
Notes
- Weather changes atmospheric pressure by about ±3% around the standard value.
- Gas flow corrections and compressor calculations always need absolute pressure.
Frequently asked questions
How do I convert gauge pressure to absolute pressure?
Add atmospheric pressure — p_abs = p_gauge + p_atm. At sea level 2 bar(g) is 3.013 bar(a), and 100 psig is 114.7 psia.
How is vacuum related to gauge pressure?
Vacuum is negative gauge pressure. A vacuum of 0.6 bar at sea level is −0.6 bar(g), or 1.013 − 0.6 = 0.413 bar(a).
Why does altitude matter?
Atmospheric pressure falls about 12% per 1,000 m near sea level, so the same absolute pressure reads differently on a gauge at altitude. Enter the altitude or override atmospheric pressure with a barometer reading.
Can absolute pressure be negative?
No — zero absolute is a perfect vacuum, so the most negative gauge reading possible is minus the atmospheric pressure.