Bar to PSI Converter
Common Conversions
| bar | psi |
|---|---|
| 0.1 | 1.45 |
| 0.5 | 7.252 |
| 1 | 14.504 |
| 2 | 29.008 |
| 5 | 72.519 |
| 10 | 145.038 |
| 20 | 290.075 |
| 50 | 725.189 |
| 100 | 1450.377 |
| 200 | 2900.755 |
| 300 | 4351.132 |
Why this conversion matters in chemistry
European-built equipment quotes pressures in bar; US-built equipment reads in psi. The same hydrogenation reactor rated at 50 bar in one catalog appears as 725 psi in the other. The factor is 14.50377 psi per bar, exact through the definitions of both units (1 bar = 100 kPa, 1 psi = 6894.76 Pa). For lab-scale work the conversion comes up most in high-pressure synthesis — a sealed reactor charged to 50 bar of hydrogen lands at 725 psi on the gauge — and in HPLC, where some pumps display column back-pressure in psi while the column manufacturer specifies the maximum in bar.
Formula
Where the factor comes from
Every other pair on this page stays inside the metric system; this one crosses into pounds and inches, and that is where the untidiness enters. The pound-force and the square inch have been exactly defined since the international yard and pound agreement of 1959 — a pound is exactly 0.45359237 kg, an inch exactly 25.4 mm — and with standard gravity fixed at 9.80665 m/s² they put 1 psi at 6894.757293168… Pa, a ratio of exact quantities that nevertheless never terminates. The bar supplies the easy half: exactly 10⁵ Pa. Dividing gives 14.5037737730… psi per bar. Notice where the non-termination comes from. The numerator is a clean power of ten, so unlike bar to atmospheres the entire mess sits on the psi side rather than being shared between two awkward integers.
Precision and significant figures
14.504 is enough for a regulator and 14.5037738 is enough for anything; digits past that describe a ratio, not a measurement. The habitual shop value of 14.5 runs low by 0.026 percent, negligible on one reading and about three-quarters of a psi once scaled to a 200 bar cylinder. A useful cross-check while you work: one psi is 68.95 mbar, so fifteen psi is just over a bar. What actually limits the result is the dial. Analog faces at reactor pressures are commonly graduated in 5 or 10 psi steps, so the fourth figure of the factor never survives being read, whatever the arithmetic offers.
Worked Examples
The IUPAC reference pressure expressed in psi — the value behind every modern thermodynamic standard state.
One standard atmosphere, the sea-level baseline both unit systems use as a calibration anchor.
A typical full compressed-gas cylinder at delivery — useful when sizing a regulator or a high-pressure manifold.
A modest reduced pressure, the kind a vacuum distillation might run at for a high-boiling solvent.
Common mistakes
14.7 and 14.5 sit next to each other
14.696 converts atmospheres and 14.504 converts bar, and the two constants get swapped constantly because both units get called standard pressure. Using 14.7 on a bar value overstates by 1.3 percent — the same gap that separates the bar from the atmosphere, arriving by a route that looks like a rounding choice rather than a unit error.
Contents and delivery are separate gauges
A two-stage regulator carries two faces, and on mixed-provenance hardware they need not share a scale — cylinder contents graduated in bar, delivery pressure in psi. Convert the contents gauge when the number you wanted was the delivery setting and the arithmetic is faultless while the answer is hundreds of times too large: 200 bar arrives as 2900 psi, standing in for a delivery of a few psi.
Differential psi needs no ambient correction
A pressure drop across a column or a filter is a difference, so a psid figure converts to bar straight across with no ambient term added. An absolute or gauge reading does not. The three suffixes look interchangeable on a spec sheet, and treating a differential as an absolute adds about 14.7 psi of pressure that was never there.