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Multiple conversions
To convert a pressure from bar to pascals (Pa), multiply by 100,000.
The bar is defined as exactly 100,000 Pa, so this is an exact conversion — a five-place decimal shift, with no empirical constant and no rounding. In megapascals the same relationship reads 1 bar = 0.1 MPa.
The reference points follow directly:
A pneumatic cylinder with a 50 mm bore runs on a 6 bar shop-air line, and the force it develops has to be calculated in newtons — which requires pascals, because a pascal is one newton per square meter:
The cylinder pushes about 120 kgf. Only in pascals do the units cancel to give newtons directly; carrying bar into the formula would produce a number with no physical meaning.
| bar | Pa |
|---|---|
| 0.001 | 100 |
| 0.01 | 1,000 |
| 1 | 100,000 |
| 1.01325 | 101,325 |
| 6 | 600,000 |
| 250 | 25,000,000 |
Bar is the unit pressures are stated in and pascal is the unit they are calculated in, so this conversion is the standard first line of a great many engineering calculations. Any formula that mixes pressure with SI mechanical quantities — force from a cylinder, stress in a vessel wall, flow through an orifice, energy stored in compressed gas — needs pascals, because the pascal is defined as N/m² and therefore cancels cleanly against meters, kilograms and seconds. Fluid mechanics makes the dependency especially visible: in Bernoulli's equation, ½ρv² produces pascals from kg/m³ and m/s, so the pressure term must be in pascals or the equation is simply inconsistent.
Two practical notes. First, the numbers get large quickly — 250 bar of hydraulic pressure is 25 million pascals — which is exactly why MPa is often preferred as the working unit in that range; 25 MPa is the same value in a more readable form, and this page's table doubles as an MPa table if you shift the decimal point five places. Second, gauge and absolute reference frames survive the conversion untouched: 6 bar gauge becomes 600,000 Pa gauge, not absolute. Gas-law calculations need the atmosphere added back, making the true figure about 701,325 Pa absolute.
To convert a pressure from bar to kilopascals (kPa), multiply by 100.
The relationship is exact by definition: the bar is defined as 100,000 Pa, which is 100 kPa. No rounding, no measured constant — shifting the decimal point two places is the conversion.
A European compressor is regulated to 6.5 bar and a maintenance sheet written for the Canadian market wants kPa:
| bar | kPa |
|---|---|
| 0.5 | 50 |
| 1 | 100 |
| 1.01325 | 101.325 |
| 2 | 200 |
| 2.2 | 220 |
| 5 | 500 |
| 7 | 700 |
| 10 | 1,000 |
Bar and kilopascal are both metric, both gauge-friendly, and separated only by convention about which industries use which. Tire pressure is the classic split: continental European placards say 2.2 bar where Canadian, Japanese and Australian placards say 220 kPa — identical inflation, different dialect. Pneumatics documentation tends to bar in Europe and kPa in SI-strict contexts; plumbing and water-supply specs mix freely. Because the factor is exactly 100, the conversion itself never introduces error — the mistakes in practice are decimal-place slips in mental math (6 bar is 600 kPa, not 60) and the perennial gauge/absolute mix-up, which this conversion, like every pressure-unit conversion, leaves untouched: 2.2 bar gauge is 220 kPa gauge, and about 321 kPa absolute.
A note on formality: the kPa is the SI-sanctioned unit; the bar is merely "accepted for use with SI", and standards bodies have been gently deprecating it for years. Industry has ignored the deprecation just as steadily — bar remains the working unit of European compressed air, diving and hydraulics — so fluency in both dialects, and the two-decimal shift between them, stays a daily necessity.
To convert a pressure from bar to megapascals (MPa), divide by 10.
Both units are decimal multiples of the pascal — 1 bar = 100,000 Pa and 1 MPa = 1,000,000 Pa — so the conversion is an exact one-digit decimal shift: move the point one place left.
A hydrogen refueling station dispenses at 700 bar, and the vessel standard you are reviewing is written in MPa:
The two families of hydrogen systems are in fact named this way: "350 bar" and "700 bar" in station marketing, "35 MPa" and "70 MPa" in the ISO and SAE standards describing the same hardware.
| bar | MPa |
|---|---|
| 1 | 0.1 |
| 6 | 0.6 |
| 10 | 1 |
| 160 | 16 |
| 350 | 35 |
| 700 | 70 |
European industrial practice runs on bar — hydraulic power units (200–300 bar), pneumatic networks (6–8 bar), pressure-relief valve set points, PN flange ratings. But the formal documents governing that same equipment speak MPa: the Pressure Equipment Directive's harmonized standards, ISO hydraulic specifications, and effectively all Japanese and Chinese technical documentation. Anyone moving between a gauge, a datasheet and a standard therefore shifts the decimal point several times a day. The direction is easy to memorize by magnitude: MPa is the bigger unit, so the number always gets smaller going bar → MPa. If a converted value grew by ten, it went the wrong way — a slip that matters when 25 bar misread as 250 bar decides a pipe schedule.
To convert from bar (bar) to hectopascal (hPa), use the following formula:
hectopascal (hPa)
= 100 × 10× bar (bar)
= 1000× bar (bar)
To convert a pressure from bar to millibar (mbar), multiply by 1,000.
The prefix does all the work: milli- means a thousandth, so a bar contains exactly 1,000 millibar. The conversion is exact, and it doubles as a hectopascal conversion for free, since 1 mbar = 1 hPa identically.
A vacuum chamber's roughing spec calls for 0.05 bar and the pump controller displays mbar:
| bar | mbar |
|---|---|
| 0.001 | 1 |
| 0.01 | 10 |
| 0.1 | 100 |
| 0.5 | 500 |
| 1 | 1,000 |
| 1.01325 | 1,013.25 |
| 2 | 2,000 |
Full bars describe pressures at or above the atmosphere; millibars exist for the territory underneath it. Meteorology occupies the top sliver of that range — the entire span of earthly weather, from the deepest recorded cyclone (~870 mbar) to the strongest Siberian high (~1,085 mbar), fits inside 0.87–1.09 bar, which is why forecasters needed the finer unit in the first place. Vacuum practice takes the rest: process steps quoted at 500 mbar, 50 mbar, 1 mbar and on down in scientific notation, where writing 5 × 10⁻⁴ bar would invite mistakes that 0.5 mbar does not. Altitude work uses the same fine graduations — cabin pressure at cruise is roughly 750 mbar, the summit of Everest about 330 mbar.
The conversion being exact, the practical hazards are neighboring-unit ones: mbar versus mmHg (a millibar is 0.750 mmHg — the units are within 25% of each other and both appear on vacuum gauges, an invitation to grab the wrong column) and mbar versus psi on mixed-market equipment. When in doubt, drop everything to pascals — 1 mbar = 100 Pa exactly — and rebuild from there.
To convert a pressure from bar to torr, multiply by 750.062.
The factor comes from the two definitions: a bar is exactly 100,000 Pa, a torr is exactly 101,325/760 Pa (≈133.322 Pa), and dividing gives 750.0617. The nearly-round result invites the useful approximation 1 bar ≈ 750 torr, good to 0.01%.
The anchor tying everything together: 1.01325 bar = 760 torr exactly — both are definitions of the standard atmosphere.
A process chamber is backfilled to 0.4 bar and the recipe sheet is written in torr:
| bar | torr |
|---|---|
| 0.001 | 0.750 |
| 0.01 | 7.50 |
| 0.1 | 75.01 |
| 0.5 | 375.03 |
| 1 | 750.06 |
| 1.01325 | 760 |
| 2 | 1,500.1 |
Bar and torr rarely share a document, because they serve opposite ends of the pressure axis — bar describes pressures at and above the atmosphere, torr describes the road down to nothing. The conversion appears exactly at the border: venting a vacuum system back to atmosphere (1.013 bar arriving as 760 torr on the chamber gauge), specifying a backfill or partial-pressure step, or translating a European pump datasheet (ultimate pressure in mbar) for an American process engineer who thinks in torr. In that last case the neater bridge is one step smaller: 1 mbar = 0.750 torr, the same factor with the decimal shifted.
One frame-of-reference note. Vacuum figures in torr are absolute pressures — zero torr is a perfect vacuum, not the room. Bar figures from compressors and pipe gauges are usually gauge readings. Converting a gauge bar figure into torr without adding the atmosphere first produces a number that means nothing in a vacuum context; the 750.062 belongs to absolute-to-absolute conversions.
To convert a pressure from bar to meters of water column (mH₂O), multiply by 10.197.
The conventional meter of water column equals 9.80665 kPa (one meter of water under standard gravity at 4 °C), and one bar is 100 kPa, so 1 bar = 100 ÷ 9.80665 = 10.197 mH₂O. The rough rule "1 bar ≈ 10 m of water" is accurate to 2% — good enough for mental checks, not for engineering submittals.
A pressure gauge at the bottom of a building's riser reads 2.5 bar, and you want to know how high the water actually stands (or could be pushed) above the gauge:
So the gauge supports a column of water about 25.5 m tall — roughly eight storeys.
| bar | mH₂O |
|---|---|
| 0.5 | 5.10 |
| 1 | 10.20 |
| 2.5 | 25.49 |
| 6 | 61.18 |
| 10 | 101.97 |
| 16 | 163.15 |
Converting bar to water column answers a physical question: how high can this pressure lift water? Divers use it in reverse constantly — every 10 m of descent adds about 1 bar, so a dive computer showing 3 bar absolute means roughly 20 m of depth plus the atmosphere above the surface. Building engineers use it to check whether street mains pressure can reach a rooftop tank without boosting; well and borehole installers translate pump pressure ratings into achievable lift. Two cautions keep the conversion honest. First, mH₂O assumes fresh water — sea water is about 2.5% denser (which is why diving tables use 10 m per bar in the sea almost exactly). Second, the conversion gives static height only; real systems lose additional pressure to pipe friction, so a 2.5 bar source will not actually deliver water at 25.5 m elevation with any flow remaining.
To convert from bar (bar) to millimeter of mercury (mmHg), use the following formula:
millimeter of mercury (mmHg)
= 100 × 10.133322× bar (bar)
= 750.0637554192106329× bar (bar)
To convert a pressure from bar to pounds per square inch (psi), multiply by 14.5038.
One bar is exactly 100,000 Pa and one psi is 6,894.76 Pa; dividing the first by the second gives 14.5038. Since one standard atmosphere is 1.01325 bar = 14.696 psi, a bar and an atmosphere differ by just 1.3% — so "1 bar ≈ 14.5 psi ≈ 1 atm" is a serviceable mental anchor across the everyday range.
A European tire placard specifies 2.5 bar and the only gauge at hand reads psi:
Inflate to 36 psi and the placard is satisfied.
| bar | psi |
|---|---|
| 0.5 | 7.25 |
| 1 | 14.50 |
| 1.01325 | 14.696 |
| 2 | 29.01 |
| 2.5 | 36.26 |
| 3 | 43.51 |
| 5 | 72.52 |
| 7 | 101.53 |
| 10 | 145.04 |
| 200 | 2,900.8 |
The bar survives because it is almost an atmosphere in a clean decimal package (10⁵ Pa exactly), and the psi survives because an enormous installed base of American gauges, fittings and specifications is written in it — so the conversion between them is the daily bread of anyone servicing equipment across markets. Espresso machines are a small but vivid example: brew pressure is quoted at 9 bar in European literature and 130 psi in American manuals, the same number twice. Hydraulics scale the stakes up — a 350 bar system is 5,076 psi, and hose or fitting ratings mixed up between the two unit systems fail in ways that are genuinely dangerous.
The gauge-versus-absolute distinction travels with the number here as everywhere in pressure work: tire, compressor and hydraulic figures in both units are gauge readings, and converting the unit does not convert the reference frame. 2.5 bar gauge is 36.3 psig; it is also about 51 psia, and which of the two a formula needs depends on whether the atmosphere participates in the physics.
To convert from bar (bar) to kilopound per square inch (ksi), use the following formula:
kilopound per square inch (ksi)
= 100 × 0.00014503768078× bar (bar)
= 0.014503768078× bar (bar)
With 0.00014503768078 is the ratio between the base units kilopound per square inch (ksi) and kilopascal (kPa).
To convert from bar (bar) to Inch of mercury (inHg), use the following formula:
Inch of mercury (inHg)
= 100 × 0.00014503768078 × 10.000491154× bar (bar)
= 29.529980572284863811× bar (bar)
With 0.00014503768078 is the ratio between the base units kilopound per square inch (ksi) and kilopascal (kPa).
The bar is a metric unit of pressure.
It is defined as exactly 100 kilopascals (kPa), or 100,000 Pascals (Pa).
Although it is not an official part of the International System of Units (SI), it is widely accepted for use with the SI. The bar is a popular unit for measuring pressure because it is very close to the average atmospheric pressure on Earth at sea level.
The term "bar" comes from the Greek word βάρος (baros), which means "weight."
The unit was introduced by British meteorologist William Napier Shaw in 1909. It is still widely used in meteorology, oceanography, and engineering.
A common point of confusion is the difference between a bar and a standard atmosphere (atm).
While they are very close in value, they are not the same:
This means 1 bar is approximately equal to 0.987 atm. Because it's so close to atmospheric pressure and is a round number (100 kPa), the bar is a very convenient unit for many applications.
The bar is a versatile unit used to measure pressure in many industrial and everyday contexts.
Common examples include: