Pressure Converter

How to Use the Pressure Converter

Enter a pressure value, choose its unit under "From" and the target unit under "To", and the converted value appears instantly. Common uses include converting tire pressure (psi to bar), weather readings (mmHg to atm), and engineering specs (kPa to psi). Use the swap button to instantly flip which unit is the source and which is the target.

Worked Examples

• 32 psi (typical car tire) to bar: 32 psi = 2.206322 bar, close to the "2.2 bar" figure printed on many non-US tire placards.
• 32 psi to kilopascal: 32 psi = 220.632233 kPa, the unit used on some European and Asian tire pressure gauges.
• 1 standard atmosphere to psi: 1 atm = 14.695949 psi, slightly higher than the 14.5038 psi you get from 1 bar, since an atmosphere is defined as a bit more than a bar.
• 120 mmHg (a normal systolic blood pressure reading) to kilopascal: 120 mmHg = 15.998686 kPa, roughly the value shown on metric blood pressure monitors.
• 1 torr to mmHg: 1 torr = 0.999999857 mmHg, a difference so small (less than one part in a million) that the two units are treated as equal in virtually every practical context.

Common Pressure Units Explained

Pascal (Pa) is the SI unit of pressure, defined as one newton of force per square meter. It's small, so kilopascal (kPa, 1,000 Pa) is more commonly used in real specifications.

Bar is a metric unit close to (but not exactly) atmospheric pressure, widely used in Europe for tire pressure, weather forecasts, and industrial hydraulics. 1 bar equals exactly 100,000 pascals.

PSI (pounds per square inch) is the standard pressure unit in the US, appearing on tire placards, plumbing specs, and compressed air equipment.

Atmosphere (atm) represents the average air pressure at sea level and is often used as a reference point in chemistry and physics rather than for everyday measurement.

mmHg and torr both originate from mercury-column barometers and manometers. mmHg remains the standard clinical unit for blood pressure, while torr is more common in vacuum engineering and lab equipment specs. The two are numerically almost identical.

Common Mistakes When Converting Pressure

The most common error is confusing gauge pressure with absolute pressure. Tire pressure gauges read "gauge pressure," meaning pressure above normal atmospheric pressure, not the true total pressure inside the tire. This converter performs a straightforward unit conversion and doesn't add or subtract atmospheric pressure, so if a source value is gauge pressure, the converted value is also gauge pressure, not absolute.

Another mistake is mixing up bar and atm because they're numerically close (1 atm is about 1.3% more than 1 bar). For casual use the difference rarely matters, but for lab work, aviation, or precise engineering specs, always use the exact figure rather than treating them as identical.

Watch decimal placement when converting between pascals and kilopascals, since a factor-of-1,000 error is easy to make when typing a large pascal value by hand.

A Quick History of Pressure Units

Pressure measurement traces back to the 1600s, when Evangelista Torricelli built the first mercury barometer and discovered that air pressure could support a column of mercury about 760 millimeters tall at sea level. That experiment is why mercury-based units like mmHg and torr (named after Torricelli himself) are still in use centuries later, even though most of science has since moved to the SI pascal, named after Blaise Pascal, another 17th-century pressure researcher. The psi and bar units came later as practical, easy-to-read alternatives for engineering and industrial work, where a pure SI pascal value would usually be an inconveniently large number.

Real-World Use Cases

Automotive: converting tire pressure specifications between psi and bar or kPa when a vehicle's manual or tire uses a different unit than your gauge.

Medical: converting blood pressure readings between mmHg and kPa when comparing a device calibrated in one unit against a reading recorded in another.

Weather and aviation: converting barometric pressure between millibars/hPa, atmospheres, and mmHg for weather reports, altimeter settings, or scientific readings.

Engineering and manufacturing: converting hydraulic, pneumatic, or compressed-gas system specs between psi, bar, and pascal when working across US and metric equipment or standards.

Frequently Asked Questions

How many psi are in 1 bar?

1 bar equals approximately 14.5038 psi. This is a common conversion for checking tire pressure specs that use different units.

What is standard atmospheric pressure?

Standard atmospheric pressure at sea level is 1 atm, which equals 101,325 pascals, 1013.25 millibars, or about 14.696 psi.

What's the difference between torr and mmHg?

They're nearly identical but not defined the same way. 1 torr is defined as exactly 1/760 of a standard atmosphere, while 1 mmHg is defined by the physical pressure of a column of mercury 1 millimeter tall under standard gravity. The two differ by less than 0.001%, so in practice they're used interchangeably in most fields, though vacuum engineering tends to prefer torr while medicine and meteorology prefer mmHg.

How do I convert my car's tire pressure between psi and bar?

Most US vehicles list tire pressure in psi (commonly 30 to 35 psi), while most vehicles outside the US list it in bar (commonly around 2.0 to 2.4 bar). Enter your psi value with psi as the From unit and bar as the To unit, or vice versa. For example, 32 psi converts to about 2.21 bar, and 2.2 bar converts to about 31.9 psi.

Why does blood pressure use mmHg instead of a more common unit?

Blood pressure has been measured with mercury manometers since the 1800s, and mmHg stuck as the standard clinical unit even after most other fields switched to metric pascals or kilopascals. A typical healthy blood pressure reading like 120/80 mmHg converts to roughly 16.0/10.7 kPa, figures you'll sometimes see on medical devices sold outside the US.

What pressure unit should engineers use for structural or fluid calculations?

Pascals and kilopascals are the SI-standard units used in most engineering formulas and international technical specifications, since they integrate directly with other SI units like newtons and square meters. Bar is common in European industrial and hydraulic contexts, while psi remains standard in US manufacturing, plumbing, and automotive work. Always match the unit your reference formula or spec sheet expects before plugging in a converted number.