How to use Pressure Converter
- Choose the Pressure basis: absolute or gauge.
- Enter the Value in the unit you have, for example 30.
- Choose Convert from, such as Pounds per square inch (psi).
- Choose Convert to, such as Bar (bar).
- The result, the pascal row and the basis note update as you change the values.
Example: Pressure Converter
Convert a gauge pressure from psi to bar.
Options
- Pressure basis
- Absolute pressure is measured from a vacuum and gauge pressure from the local atmosphere. The choice is carried to both sides of the conversion, and the difference between them is never guessed.
- Decimal places
- Sets display rounding to 0, 2, 4, 6 or 8 places. Four places is the default because the psi and bar factors are long decimals.
Supported inputs and limits
Where your input is processed
This tool processes your input in this browser. Your text and files are not uploaded to UseFreeTools. Check this tool's limits for anything it may save on your device.
Why the basis is asked before the number
The conversion factor between two pressure units is a ratio, so it is identical on absolute and gauge readings. That is exactly the trap: a correct-looking ratio can move a reading from one basis to the other without anyone noticing. Asking for the basis first and printing it with the result keeps a gauge figure gauge and an absolute figure absolute, and it also lets the tool reject a negative absolute reading, which cannot exist.
NIST Special Publication 811, Appendix B.8: standard atmosphere factor
Where each pressure factor comes from
The pascal is the SI unit, so it is the base here. One bar is exactly 100,000 Pa and one standard atmosphere is exactly 101,325 Pa, both by definition. A torr is 101325/760 Pa. One pound per square inch is the standard pound force of 4.4482216152605 N spread over one square inch of 0.00064516 square meters, which is about 6894.757293 Pa, and one kilogram-force per square centimeter is exactly 98066.5 Pa.
NIST Special Publication 811, Appendix B.8: bar, atmosphere, torr, psi and kilogram-force factors
Questions about Pressure Converter
Does the tool convert gauge pressure to absolute pressure?
No. It converts between units and keeps the basis you selected on both sides. Turning gauge pressure into absolute pressure needs the local atmospheric pressure added, which varies with altitude and weather, so that step is left to you.
What is the difference between absolute and gauge pressure?
Absolute pressure is measured from a full vacuum, so it can never be negative. Gauge pressure is measured from the surrounding atmosphere, so it reads zero when the two are equal and goes negative in a vacuum. The gap between them is the local atmospheric pressure, about 101.325 kPa at sea level and lower at altitude.
Is one bar the same as one atmosphere?
They are close but not equal. One bar is exactly 100,000 Pa, while one standard atmosphere is exactly 101,325 Pa, which is about 1.01325 bar. Pick the unit your source used.
Why is there no millimeters of mercury unit?
A torr is exactly 1/760 of a standard atmosphere, while a conventional millimeter of mercury is very slightly larger. Offering both would invite a mix-up, so the page offers the torr and says so on the result.
Can I enter a tire pressure?
Yes, if you know whether the figure is gauge or absolute. Tire gauges almost always read gauge pressure, so choose Gauge pressure first, then convert between psi, bar or kPa.