Torr to Bar Converter
Common Conversions
| torr | bar |
|---|---|
| 1 | 0.001333 |
| 10 | 0.01333 |
| 50 | 0.06666 |
| 100 | 0.13332 |
| 200 | 0.26664 |
| 400 | 0.53329 |
| 500 | 0.66661 |
| 600 | 0.79993 |
| 750.062 | 1 |
| 760 | 1.01325 |
| 1000 | 1.33322 |
Why this conversion matters in chemistry
Sublimation apparatus and vapor-pressure tables stay in torr by long convention; modern safety documentation and IUPAC-aligned thermodynamic references run in bar. The constant of 0.001333224 bar per torr falls out of 760 torr per atmosphere and 1.01325 bar per atmosphere. A sublimation run held at 0.5 torr is 6.66 × 10⁻⁴ bar — the value a vacuum-system spec sheet might list once a group has standardized on SI-derived units. Multiplying is decimal arithmetic but the conversion is the bookkeeping at the boundary between mercury-column tradition and modern reporting.
Formula
Where the factor comes from
Neither unit was ever defined with reference to the other, and each was built to come out round in a system the other ignores. The bar is round in pascals — exactly 10⁵ of them, picked for convenience rather than derived from anything physical. The torr is round in atmospheres — exactly 1/760 of the defined 101325 Pa. Put the two together and the factor is 101325 divided by 760 × 10⁵, giving 1.3332236842… × 10⁻³ bar per torr. Read the other way it is 750.0616827 torr per bar, and that reciprocal is the real content of the page: a bar falls about ten torr short of an atmosphere, because 101325 Pa sits 1.325 percent above 10⁵ Pa. Both ingredients are exact by definition, so the factor is exact and endlessly non-terminating at once.
Precision and significant figures
The six figures in 0.001333224 exceed anything this pair needs; 1.3332 × 10⁻³ is within twenty parts per million, and four figures cover any gauge in service. Watch what the leading zeros do to a written result, though. A vapor pressure recorded as 23.8 torr carries three figures and becomes 0.0317307 bar if a calculator is copied straight across, now claiming six. Trim it to 0.0317. Care matters here because of where these numbers go next: standard-state thermodynamics puts pressures relative to 1 bar inside a logarithm, and at 298 K a one percent error in p moves RT ln(p/p°) by roughly 25 J/mol — small alone, less so across a multi-term calculation.
Worked Examples
Standard atmospheric pressure expressed in bar — the calibration anchor in both unit systems.
Exactly 1 bar in torr — the IUPAC reference pressure for tabulated standard-state values.
The factor itself — useful as a quick mental check on a vacuum-gauge reading.
The vapor pressure of water at 25 °C — the value behind any gas collected over water calculation done in bar.
Common mistakes
A bar is 750 torr, not 760
The 760 is so familiar that it gets reused for the bar without a second thought, and the resulting figure is 1.325 percent off every time. A 600 torr reading is 0.7999 bar using the correct 750.06, and 0.7895 bar using 760 — a difference that will not look wrong on the page but biases a whole set of values in one direction. Keep the two anchors separate.
Older tables use a 1 atm standard state
IUPAC moved the standard pressure for tabulated thermodynamic data from 1 atm to 1 bar in 1982. Standard entropies of gases differ between the two conventions by R ln(1.01325), about 0.11 J/(mol·K), with corresponding shifts in formation Gibbs energies. Converting a pressure into bar and then reading it against a pre-1982 table quietly mixes reference states; check which convention a compilation was built on.
The bar is not a coherent SI unit
It is a convenient decimal multiple of the pascal, not part of the SI proper, so any equation written for coherent units still wants pascals. A 100 torr reading is 0.1333 bar and 13332 Pa; drop the bar value into an expression carrying R = 8.314 J/(mol·K) and the pressure is a hundred thousand times too small, with nothing in the units to object.