PSI to Bar Converter
Common Conversions
| psi | bar |
|---|---|
| 1 | 0.0689 |
| 5 | 0.3447 |
| 10 | 0.6895 |
| 14.696 | 1.013 |
| 25 | 1.724 |
| 50 | 3.447 |
| 100 | 6.895 |
| 200 | 13.79 |
| 500 | 34.47 |
| 1000 | 68.95 |
| 2000 | 137.9 |
| 3000 | 206.8 |
Why this conversion matters in chemistry
Pressure measurement sits at an awkward seam between imperial and metric conventions. US-sourced equipment reads in psi; European spec sheets and modern SI-aligned references use bar. A 1000 psi gas line is 68.95 bar; a 100 psi benchtop hydrogenation is 6.9 bar. The factor is 0.069 going from psi to bar, close enough to 1/15 that you can rough-estimate by dividing psi by 15 and land within 3%. Regulators sold internationally typically label both scales for this reason, which lets you cross-check mentally without reaching for a calculator.
Formula
Where the factor comes from
The bar was defined to be a round number of pascals — exactly 10⁵ — rather than to match anything physical, and that makes this the least eventful conversion in the pressure family. Work the psi out from its own definitions (a pound-force of exactly 4.4482216152605 N over exactly 6.4516 × 10⁻⁴ m², so 6894.757293… Pa) and then move the decimal point five places: 0.06894757293… bar per psi. The digits are identical either way; only their position changes. Both ingredients are exact by definition, so the factor inherits no measurement uncertainty, though the decimal runs on and is never written out whole. The bar is not part of the SI proper; it survives as a convenient decimal multiple of the pascal rather than as a coherent SI unit.
Precision and significant figures
0.0689476 is high by four parts in ten million, and even a blunt 0.069 costs 0.076 percent, which a dial graduated in whole bar will never show. The rule-of-thumb division by 15 is a different animal: it runs 3.3 percent low every single time, biasing a set of readings in one direction instead of scattering them. Fine for deciding whether a regulator is roughly in range, wrong for anything that ends up tabulated. Metric dial gauges are typically specified as a percentage of full scale in the one to two-and-a-half percent band, so on a 250 bar face that is somewhere between two and six bar wherever the needle happens to sit.
Worked Examples
Sea-level atmospheric pressure, written in both units. The useful anchor: 1 atm ≈ 1 bar, and both work out to about 15 psi.
A full nitrogen cylinder. The number you'd see on the high-pressure gauge of a Schlenk-line supply regulator.
A moderate elevated pressure typical of benchtop catalytic hydrogenation work.
A full hydrogen cylinder, or the kind of supply pressure high-pressure hydrogenation and fuel-cell research work with.
Common mistakes
0.0689476 and 6.89476 are the same digits
A bar is 10⁵ Pa and a kilopascal 10³, so the psi-to-bar and psi-to-kilopascal factors carry identical digits two decimal places apart, and they get swapped constantly. When a converted result lands in the hundreds where you expected single digits, you have produced kilopascals wearing a bar label. A 100 psi hydrogenation is 6.9 bar or 689 kPa; strip the unit off and nothing in the arithmetic distinguishes them.
Rough-vacuum equipment reads in millibar
Diaphragm and rotary-vane pump specifications, and most rotary-evaporator controllers outside the US, are written in millibar. A converted result of 0.02 bar is 20 mbar and 0.29 psi — three ways of writing one pressure, only one of which matches the controller's entry field. The thousandfold step is easy to skip when the bar value is already a small decimal.
kgf/cm² dials are not bar dials
Older European and Asian gauges are often graduated in kilograms-force per square centimeter, exactly 98066.5 Pa, which is 0.980665 bar or 14.223 psi. The face may say kg/cm² in small type while the numbers look exactly like a bar scale. Comparing a psi-derived bar figure against such a dial leaves a systematic 1.9 percent gap that is easy to blame on the gauge instead.