All factors here reduce to pascals, the SI unit of pressure, sourced from NIST’s own published conversion tables.
How it works
Exact and near-exact factors
1 bar = 100,000 Pa exact · 1 atm = 101,325 Pa exact
1 psi ≈ 6894.757293 Pa · 1 torr = 101,325 ÷ 760 Pa exact
Bar and atmosphere are both defined directly in pascals, so those two are exact. PSI is derived here from two other exact constants already used on this site — the exact pound-force and the exact inch — which is slightly more precise than NIST’s own rounded table entry for psi, not a second, independent source of error.
How to use this calculator
- Type a pressure into any field.
- The rest update — kilopascals, bar, PSI and atmospheres up front; pascals and torr/mmHg behind “More units”.
Frequently asked questions
Is torr the same as mmHg?
Close enough that they are used interchangeably in almost all practical contexts — the modern legal definition of a torr (1/760 of a standard atmosphere) and the physically measured “millimetre of mercury” agree to about six decimal places, far closer than any measurement instrument can distinguish.
Why is 1 atmosphere exactly 101,325 pascals?
Because it is defined that way — the standard atmosphere is a fixed reference value, not a measured average of real-world air pressure, which genuinely varies with weather and altitude.
Is PSI an exact conversion?
It composes two other exact constants — the pound-force and the inch — so the result carries no more rounding error than those two already do, even though NIST’s own summary table for psi is itself rounded to six figures.
What is bar used for, compared to PSI or atm?
Bar is common in weather reporting and in much of the world’s engineering and diving contexts, precisely because 1 bar is close to (but not the same as) 1 standard atmosphere, making it an intuitive round number for everyday pressures.
