Bar to PSI Converter

The bar to psi converter is a fast, exact pressure-conversion tool that moves any reading between bar and pounds per square inch (psi) in both directions, with live bonus read-outs in kilopascals (kPa), standard atmospheres (atm), and torr (mmHg). Type a value into any of the five fields and the other four update instantly, with no rounding ambiguity and no measurement uncertainty, because every conversion factor on this page traces back to a single definition: 1 bar = exactly 100 000 pascals (NIST SP 811, BIPM SI Brochure 9th ed., ISO 80000-4). It is built for the everyday situations where you are handed a pressure figure in one unit and need the others immediately: a European tyre-pressure placard that prints 2.3 bar next to a North American service manual that quotes 33.4 psi; a scuba tank gauge that reads 200 bar and a decompression table that requires the same pressure in psi; an espresso machine manual that lists 9 bar as the standard brew pressure and a coffee-forum post that insists on psi; a hydraulic-system specification stamped 250 bar alongside a US calibration certificate that gives 3625.94 psi; or a research-paper appendix that uses bar throughout while the supplementary information gives everything in atm or torr.

The converter assumes the modern international bar, which has been exactly 100 000 pascals since 1954, when the 10th General Conference on Weights and Measures (CGPM) adopted the figure originally proposed by the Comité International des Poids et Mesures (CIPM). NIST Special Publication 811 ("Guide for the Use of the SI Units"), the BIPM SI Brochure (9th edition, 2019, §2.3.3), and the IUPAC Green Book (3rd edition, 2007) all cite the same constant. The bar was deliberately chosen to be close to, but not exactly equal to, the standard atmosphere (1 atm = 101 325 Pa = 1.01325 bar). That 1.325% difference matters in precise work: a 1 atm reading is 1.01325 bar, not exactly 1 bar, and the converter's atm row makes the difference explicit. The psi value comes from the NIST-exact definition 1 psi = 6 894.757293168 Pa, which gives 1 bar = 14.5037738 psi to eight significant figures. The torr row uses the CIPM 1980 constant 1 torr = 133.322387415 Pa (reaffirmed 2007; ISO 80000-9:2009; NIST SP 811 §B.8), so 1 bar = 750.0617... torr. None of these factors are rounded approximations; each one is derived from the exact 100 000 Pa/Pa definition of the bar through exact division.

How to use this converter

1. Type the numeric value you want to convert into the Bar (bar) field, the Pounds per square inch (psi) field, the Kilopascals (kPa) field, the Atmospheres (atm) field, or the Torr (torr) field. Decimal values are accepted, including sub-bar values such as 0.001 bar (= 100 Pa = 0.0145037738 psi) and sub-psi values such as 1 psi (= 0.0689476 bar).
2. The other four fields update automatically as you type. For the Bar To Psi, The update is recomputed on every keystroke, so the panel always reflects the latest value.
3. Read the Result in bar row and the Result in psi row to see the same pressure quoted in the two units that give this tool its name.
4. Read the Also in kilopascals, Also in atmospheres, Also in torr (mmHg), and Also in pascals rows for the four most common cross-unit read-outs at the same time. The pascals row uses integer formatting with thousand-separators because that is the canonical SI unit.
5. Use the ⇄ swap button when you want to flip the orientation between bar and psi: the value in the psi field moves to the bar field and vice versa.
6. Click Copy bar or Copy psi to put the value on the clipboard in your chosen unit.
7. To verify a conversion against a printed gauge or table, enter the printed value in any field and read the result.

the Bar To Psi runs entirely in the browser. For the Bar To Psi, Inputs are not stored, not transmitted, and not associated with any account.

The formulas

The conversion between bar and every other pressure unit on this page is defined rather than measured, so there is a single exact factor for each direction:

Primary conversion (bar ⇄ psi):

1 bar = 100 000 Pa exactly

1 psi = 6 894.757293168 Pa exactly (NIST SP 811)

Therefore 1 bar = 100 000 / 6 894.757293168 psi = 14.5037738007... psi

To convert bar → psi: multiply by 14.5037738.

psi = bar × 14.5037738

To convert psi → bar: divide by 14.5037738 (or equivalently multiply by 0.0689476...).

bar = psi / 14.5037738

Bar ⇄ kilopascals (kPa):

1 bar = 100 000 Pa = 100 kPa exactly

kPa = bar × 100

bar = kPa / 100

Bar ⇄ atmospheres (standard atm):

1 atm = 101 325 Pa exactly (NIST SP 811, BIPM SI Brochure 9th ed.)

1 bar = 100 000 / 101 325 atm = 0.9869232667... atm

atm = bar × 0.9869232667...

bar = atm × 1.01325 (exactly)

Bar ⇄ torr (mmHg):

1 torr = 133.322387415 Pa exactly (CIPM 1980, reaffirmed 2007; ISO 80000-9:2009)

1 bar = 100 000 / 133.322387415 torr = 750.0616827... torr

torr = bar × 750.0616827...

bar = torr × 0.00133322387415...

Bar ⇄ pascals (Pa):

1 bar = 100 000 Pa exactly (definition)

Pa = bar × 100 000

bar = Pa / 100 000

To go from bar to any of these units, multiply the bar value by the factor above. To go from any of these units to bar, divide by the factor above.

Worked examples

Example 1, Car tyre pressure. A European tyre placard recommends 2.3 bar for the front tyres of a family hatchback. Reading the calculator:

P = 2.3 bar = 2.3 × 14.5037738 = 33.3587 psi P = 2.3 bar = 230 kPa = 2.269 atm = 1 725.142 torr

The psi reading (33.36 psi) is what a North American driver would inflate to with a typical US tyre gauge. The 2.3 bar figure is the same physical pressure: a tyre pumped to 2.3 bar holds about 2.27 standard atmospheres of gauge pressure above the surrounding atmosphere.

Example 2, Scuba tank at the surface. A recreational scuba cylinder is filled to 200 bar at the dive shop:

P = 200 bar = 200 × 14.5037738 = 2 900.7548 psi P = 200 bar = 20 000 kPa = 197.385 atm = 150 012.336 torr

The psi reading (about 2 901 psi) is what an American-built hydrostatic test rig would print on the cylinder's VIP (visual inspection) sticker. The atm reading (about 197 atm absolute) is the figure that a decompression algorithm plugs into its gas-loading equations.

Example 3, Espresso machine brew pressure. A modern espresso machine is rated at 9 bar of brew pressure, the industry-standard target for a properly extracted shot:

P = 9 bar = 9 × 14.5037738 = 130.5340 psi P = 9 bar = 900 kPa = 8.882 atm = 6 750.555 torr

The psi reading (about 130.5 psi) is the figure a North American barista would expect to see on a third-party pressure gauge plumbed into the group head. Note that 9 bar is not the same as 9 atm: 9 atm would be 9.118 bar, or about 132 psi.

Example 4, Vacuum and rough pressure. A laboratory roughing pump pulls a chamber down to 0.001 bar:

P = 0.001 bar = 0.001 × 100 000 = 100 Pa P = 0.001 bar = 0.0145 psi = 0.1 kPa = 0.000987 atm = 0.7501 torr

This is roughly 1 millitorr, a typical base pressure for an oil-sealed rotary roughing pump before the high-vacuum stage takes over.

Example 5, Hydraulic press rating. A hydraulic press is rated at 250 bar of working pressure on its European nameplate:

P = 250 bar = 250 × 14.5037738 = 3 625.9434 psi P = 250 bar = 25 000 kPa = 246.731 atm = 187 515.421 torr

The psi figure (about 3 626 psi) is what a US spec sheet would print alongside the same 250 bar rating. The two numbers describe the same working pressure with no rounding: the bar/psi factor (14.5037738) is exact to ten significant figures because both units trace back to the pascal.

Example 6, Round-trip identity. Any pressure expressed in bar and converted to psi and back, with no intermediate rounding, returns the original number to the precision of the stored value:

P = 2.5 bar → psi = 2.5 × 14.5037738 = 36.2594345 → bar = 36.2594345 / 14.5037738 = 2.5 bar

The defining property of an exact conversion: there is no measurement uncertainty in either direction, only the precision of the floating-point representation on screen.

Where bar ⇄ psi shows up

Automotive tyres. Continental Europe and most of the world quote tyre pressures in bar; the US and Canada quote in psi. A 2.3 bar placard reading is 33.36 psi, and the two gauges are reading the same physical pressure. The bar/psi converter is the natural place to confirm the equivalence when you swap wheels between a European car and a North American one.

Scuba and paintball cylinders. Recreational scuba cylinders are filled to roughly 200 bar (about 2 900 psi); paintball tanks are filled to roughly 250 bar (about 3 626 psi); technical-diving bailout cylinders are sometimes rated to 300 bar (about 4 351 psi). Hydrostatic test certificates vary by jurisdiction between bar and psi.

Espresso and coffee machines. The standard brew pressure for espresso is 9 bar (about 130.5 psi). North American espresso machine spec sheets often quote psi; European spec sheets quote bar; coffee-forum posts and third-party gauges usually quote either interchangeably. The bar/psi converter makes the cross-check immediate.

Hydraulics and pneumatics. Industrial hydraulic systems are typically rated in bar (250 bar for a high-pressure press, 350 bar for a high-pressure die-casting machine, 700 bar for ultra-high-pressure water-jet cutting). North American hydraulics literature often uses psi (3 626 psi, 5 076 psi, 10 153 psi respectively). Compressed-air systems are rated in bar (8 bar shop air, 10 bar truck-air brake pressure, 350 bar hydrogen vehicle tanks).

Scuba diving. Depth-rated equipment cites hydrostatic pressure in bar (10 m of seawater = 1 bar gauge pressure, plus 1 bar of atmospheric pressure at the surface = 2 bar absolute). Pressure gauges, tank-pressure gauges, and buoyancy compensator inflators are calibrated in bar. North American dive literature often uses psi for the same readings.

Aviation. Pneumatic systems in aircraft are typically rated in psi (cabin pressurisation, hydraulic actuators, oxygen systems). Ground-support equipment and European aviation documentation quote bar. A 3 000 psi hydraulic system is about 207 bar.

Vacuum science. The torr (mmHg) row is the practical unit for sub-atmospheric work; the bar/psi rows are the practical units for positive-pressure work. The converter handles the whole range from rough vacuum (10⁻³ bar) to high-pressure hydraulics (10³ bar) without changing tools.

Meteorology. Surface pressure is reported in hectopascals (hPa, identical to millibars), a 1 013.25 hPa reading is exactly 1 atm, exactly 1.01325 bar, exactly 14.6959 psi, and exactly 760 torr. The converter's atm and torr rows give the cross-checks.

Common mistakes when converting bar and psi

Mistake 1: Treating "1 bar ≈ 1 atm" as exact. Standard atmosphere pressure is 101 325 Pa, but 1 bar is exactly 100 000 Pa. The difference (1.325%) shows up in any NIST-traceable calibration: a 1 atm barometer reads about 1.01325 bar, not exactly 1 bar. The converter's atm row makes the difference explicit.

Mistake 2: Using the wrong psi definition. The international foot-and-pound definitions give 1 psi = 6 894.757293168 Pa exactly (NIST SP 811). The older "metric horsepower" or "technical psi" definitions of years past are obsolete; modern data should always use the NIST factor. The converter uses the modern factor and produces 1 bar = 14.5037738 psi to eight significant figures.

Mistake 3: Confusing gauge and absolute pressure. A "30 psi tyre" is 30 psi above atmospheric, not 30 psi absolute. The same physical pressure in bar is about 2.07 bar gauge. If your source says "absolute" (psia, bara), do the subtraction before comparing; if it says "gauge" (psig, barg), leave it alone. The converter is a pure unit-conversion tool and works on whichever reference you supply.

Mistake 4: Rounding the bar/psi factor to 14.5. A 14.5/14.5037738 difference is 0.026%, which is 0.009 psi on a 35 psi tyre reading. On a 3 000 psi scuba cylinder, rounding 14.5037738 to 14.5 loses about 0.8 psi, enough to fail a hydrostatic-test tolerance. Use the full factor.

Mistake 5: Reading "bar" as a unit of force. Pressure is force per unit area. "Bar" is a unit of pressure (force per area), not a unit of force. A force of "1 bar" makes no sense; what you usually want is a pressure of "1 bar" applied over an area to compute force (F = P × A).

Mistake 6: Mixing up psi, psia, and psig. psi is the unit; psia is psi absolute (zero at perfect vacuum); psig is psi gauge (zero at local atmospheric). 14.7 psia is about 0 psig at sea level, because atmospheric pressure is about 14.7 psi. The converter handles the psi reading you give it; subtract local atmospheric pressure (about 14.7 psi at sea level) before converting if you want the absolute figure.

Mistake 7: Forgetting to convert SI prefixes. The pascal is the SI unit, but engineering data often quotes kilopascals (kPa), megapascals (MPa), or hectopascals (hPa). Converting "1 013.25 hPa" to bar requires dividing by 1 000 (since 1 hPa = 100 Pa = 0.001 bar), not by 100. A common error is to skip the 1 000 and get "1 bar ≈ 1 013 hPa", which is off by a factor of 1 000.

Mistake 8: Round-trip rounding error. Converting 1 bar to psi gives 14.5037738 psi, and converting back gives 1 bar exactly because 14.5037738 is exact to ten figures. But rounding the intermediate psi figure to "14.5" before converting back gives 14.5 / 14.5037738 = 0.99973 bar, a 0.00027 bar error that grew from a four-figure rounding choice. Use the full stored value at every step.

Mistake 9: Comparing bar and "bar absolute" / "bar gauge" across documents. Some European pneumatic documents use "bar" as gauge pressure (zero at local atmospheric) and some use "bar" as absolute pressure (zero at perfect vacuum). A 2 bar gauge reading is about 3 bar absolute at sea level. Confirm which convention your source uses before comparing readings across documents.

Mistake 10: Assuming the bar is the same as the technical atmosphere. The technical atmosphere (CIPM 1954, 1 kgf/cm²) is 98 066.5 Pa, about 1.93% smaller than the bar. The "at" symbol survives in older DIN standards, but the bar has replaced it in modern European engineering practice. The converter uses the modern international bar (100 000 Pa exactly), which is what current technical data sheets expect.

Frequently Asked Questions

What is the exact relationship between bar and psi? The bar is defined as exactly 100 000 pascals by the CIPM in 1954, ratified by the 10th General Conference on Weights and Measures (CGPM), and confirmed by NIST Special Publication 811 and the BIPM SI Brochure (9th edition, 2019, §2.3.3). The psi is defined as exactly 6 894.757293168 pascals (NIST SP 811, derived from the 1959 international yard and pound agreement). Therefore 1 bar = 100 000 / 6 894.757293168 psi = 14.5037738007... psi, an exact relationship that traces through the pascal with no measurement uncertainty.

Why do we have both bar and psi? The bar is the metric unit used in most of the world for everyday pressure: tyre placards, scuba gauges, espresso machine ratings, hydraulic-system nameplates, and compressed-air systems. The psi is the imperial/US unit used in the same contexts in the United States, Canada, and a handful of other countries. Because both units are defined in terms of the pascal, the SI base unit of pressure, converting between them is exact: there is no rounding error, no measurement uncertainty, and no ambiguity about which version of the units to use.

Where does the figure 100 000 Pa for the bar come from? It is not measured, it is defined. The bar was introduced in 1909 by the Norwegian meteorologist Vilhelm Bjerknes as a convenient approximation to typical sea-level atmospheric pressure (about 1 013.25 millibar). In 1954, the CIPM fixed the bar at exactly 100 000 Pa so that 1 bar = 10⁵ Pa would be a tidy power-of-ten reference, and the CGPM ratified the definition. Today's actual sea-level atmospheric pressure fluctuates around 101 325 Pa (1.01325 bar) by a few percent on extreme weather days.

Is the bar an SI unit? No. The bar is a metric unit accepted for use with the SI by the BIPM SI Brochure (9th edition, §4.1), but it is not an SI unit itself. The SI unit of pressure is the pascal (Pa), where 1 Pa = 1 N/m². The bar survives because it is a convenient size for engineering pressures: 1 bar is roughly atmospheric pressure, 100 bar is a high-pressure hydraulic system, 1 000 bar is an ultra-high-pressure water-jet cutter. The SI kilopascal (kPa) and megapascal (MPa) cover the same ranges in SI terms.

What is the difference between bar, mbar, and μbar? 1 bar = 1 000 millibar (mbar) = 1 000 000 microbar (μbar) exactly, because the bar is exactly 100 000 Pa and the millibar is exactly 100 Pa (the millibar and the hectopascal are numerically identical). Meteorologists traditionally use millibars or hectopascals; engineers use bar or megapascal; vacuum scientists use millibar or torr depending on the regime. The converter's kPa and torr rows cover the most common cross-checks.

Can I use this converter for vacuum measurements? Yes. The bar is not restricted to positive pressures; it covers the full range from ultra-high vacuum (10⁻¹² bar or below) to gigapascal geology (10⁴ bar). Below about 1 mbar, the torr is the more practical unit, and 1 torr = 1/760 atm exactly, so 1 bar = 750.0617... torr and 1 mbar = 0.750062 torr. The converter's torr row gives the same figure at standard resolution.

Should I round the result to a sensible number of decimal places? It depends on the application. For a tyre placard reading, two decimal places is appropriate (2.30 bar or 33.36 psi). For a NIST-traceable calibration, use the full stored value at every step, even a four-figure round-trip accumulates a pascal of rounding error. For scuba and hyperbaric applications, one decimal place in bar is usually enough. The calculator shows eight decimal places in bar and psi, six digits in kPa and torr, and the full integer figure in pascals, so you can pick the precision your work needs.

Is 1 bar the same as 1 bar absolute (bara)? For most engineering work, "bar" defaults to "bar gauge" (zero at local atmospheric), unless the context makes clear the value is absolute (zero at perfect vacuum). Scuba and hyperbaric work distinguishes bar absolute (bara) from bar gauge (barg), gauge pressure reads zero at the surface (so 1 barg is 1 bar above atmospheric, or 2 bara total), while absolute pressure reads 1 bar at the surface. The converter here is a pure unit-conversion tool and works on whichever reference you supply; subtract local atmospheric pressure (about 1.01325 bar) from a gauge reading before converting if you want the absolute figure.

When did the bar change from 1 bar = 1.01325 atm? It never changed. The bar has been exactly 100 000 Pa since 1954; the standard atmosphere has been exactly 101 325 Pa since the same year. The two were deliberately defined to differ by about 1.325%, and that ratio has not changed. The only equivalent is the adoption of the bar in some industrial standards where the technical atmosphere (98 066.5 Pa) had been used, but the bar itself has been constant for seventy years.

How do I convert between bar and atm? 1 bar = exactly 0.9869232667... atm (because 1 atm = 101 325 Pa and 1 bar = 100 000 Pa). Therefore to convert bar to atm, multiply by 0.9869232667...; to convert atm to bar, multiply by 1.01325 (exactly). The two units differ by about 1.3%, and a 1 atm reading is 1.01325 bar, not exactly 1 bar.

How do I convert bar to kPa (kilopascals)? 1 bar = exactly 100 kPa. Therefore to convert bar to kPa, multiply by 100; to convert kPa to bar, divide by 100. The conversion is exact because both the bar and the kilopascal are defined as exact multiples of the pascal (1 bar = 100 000 Pa, 1 kPa = 1 000 Pa).

How do I convert bar to torr? 1 bar = 750.0616827... torr. This comes from the CIPM 1980 constant 1 torr = 133.322387415 Pa (reaffirmed 2007; ISO 80000-9:2009; NIST SP 811 §B.8). To convert bar to torr, multiply by 750.0616827...; to convert torr to bar, multiply by 0.00133322387415... The factor is exact to ten significant figures because both the bar and the torr are defined in terms of the pascal with no measurement uncertainty.

Why is there no factor of 100 between bar and mbar in some references? There is a factor of 1 000 between bar and millibar (1 bar = 1 000 mbar exactly), because both are defined in terms of the pascal. Some older texts use the term "millibar" loosely to mean either a thousandth of a bar or a hectopascal; the two are numerically identical (1 mbar = 1 hPa = 100 Pa) so the loose usage rarely matters in practice. The converter shows kPa alongside bar, so 1 bar = 100 kPa is unambiguous.

Also try these free tools:

• PSI to Bar Converter
• Atmospheres to Pascals Converter
• Torr to Pascals Converter
• Pressure Converter