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Pressure Converter

Quick picks

Result

1 Bars = 14.5038 Pounds per square inch (psi)

Estimates for educational purposes — not financial, medical, or legal advice. See terms.

Convert between nine pressure units in one tool, routed through pascals as a canonical base. Source and target dropdowns cover everything from laboratory vacuum work (mmHg, torr) through everyday pressures (kPa, bar, psi, atm) to high-pressure industrial (MPa). Quick-pick buttons jump to the five most commonly-requested pair conversions.

The formula

Every conversion routes through pascals:

target=source⋅Pa per sourcePa per target\text{target} = \text{source} \cdot \frac{\text{Pa per source}}{\text{Pa per target}}

Using a canonical base keeps the code simple and exposes the unit factors as a single lookup table — adding a new unit is one entry in that table, not a new pair-specific formula.

Supported units

From smallest typical value to largest:

  • Pascal (Pa) — SI base unit. 1 Pa = 1 N/m². The sensitivity is such that a single page of paper weighing 4.5 g spread over 1 m² produces about 0.04 Pa — Pa is almost never used alone for practical pressures because the numbers get huge.
  • Hectopascal / millibar — NOT in this tool directly (use kPa / 10), but worth mentioning: weather reports use hPa where typical sea-level pressure is 970–1040.
  • Kilopascal (kPa) — 1000 Pa. Common SI unit for tires, medical gauge pressure, general engineering.
  • Bar — exactly 100,000 Pa. Slightly smaller than 1 atmosphere. European tire and diving pressures.
  • Atmosphere (atm) — exactly 101,325 Pa. “Standard atmosphere” since the 1954 CIPM definition.
  • psi — 6,894.76 Pa. US imperial unit for tires, compressors, pressure cylinders.
  • mmHg / torr — ≈ 133.32 Pa. Blood pressure, chemistry vacuum, legacy barometers.
  • inHg — ≈ 3,386.39 Pa. US aviation altimeters and home barometers.
  • Megapascal (MPa) — 1,000,000 Pa. Industrial hydraulics and material strength.

The mmHg vs torr distinction

This is the one non-trivial subtlety in the tool. Both units have a value of about 133.32 Pa, but:

  • Torr is defined as exactly $\frac{101325}{760}$ Pa, so by definition 760 torr = 1 atm exactly.
  • Millimetres of mercury is defined by the physics of a mercury column at 0 °C under standard gravity: 133.322387415 Pa.

The difference is about 1 part in 10^7 — nothing cares about it except the most precise metrology work. In daily practice, medical blood pressure (120/80 mmHg) and chemistry vacuum (10 torr) use the two units interchangeably. This converter gives you the mathematically correct result for each.

Example: weather pressure

A typical sea-level reading of 1013 hPa is:

  • 1013 hPa = 101.3 kPa = 1.013 bar = 0.9998 atm = 14.696 psi = 759.7 mmHg = 29.912 inHg

The atm value is very close to 1 because 1013 hPa is within rounding of the 1954 CIPM definition. The US uses inHg on home barometers (hence “30.00 inches of mercury, falling” on weather broadcasts); Europe uses hPa or mbar.

Example: car tire pressures

  • 32 psi (US typical car) = 220.63 kPa = 2.2063 bar = 2.177 atm = 1,654 mmHg
  • 2.2 bar (European typical) = 31.91 psi = 220 kPa

Manufacturers pick a round number in whichever unit their target market uses, and the “equivalent” in the other unit is approximate. A 32 psi sticker and a 2.2 bar sticker are roughly but not exactly the same physical pressure.

Example: medical blood pressure

  • 120/80 mmHg (typical adult) = 16.00/10.67 kPa = 2.321/1.547 psi

Medical blood pressure is reported in mmHg worldwide, one of the last holdouts where the older unit dominates. It’s unlikely to change — too many instruments, charts, textbooks, and trained clinicians know the mmHg values by heart.

Example: industrial pressures

  • Hydraulic system: 250 bar = 25 MPa = 3,626 psi
  • Water jet cutting: 4,000 bar = 400 MPa = 58,015 psi
  • SCUBA tank (Europe): 200 bar = 20 MPa = 2,900.75 psi
  • Steam locomotive boiler: 12–15 bar = 1.2–1.5 MPa = 174–218 psi

For anything above 100 bar, engineers typically switch to MPa to keep the numbers readable. Below that, bar or kPa is more natural. The psi scale goes higher before getting unwieldy (thousands of psi are still pronounceable) which is why US hydraulic systems often stay in psi longer than the metric equivalent would.

What this tool does not do

It doesn’t distinguish gauge vs absolute pressure. Gauge pressure is relative to local atmospheric pressure (a tire at 32 psi gauge is 32 psi above atmospheric); absolute pressure is relative to a perfect vacuum. The converter operates on scalar values — you decide whether the input is gauge or absolute, and the output keeps whichever convention you started with.

It doesn’t handle hPa / mbar as separate units because they’re just bar × 1000 / 100,000 = kPa / 10 — kPa covers the same range at slightly different precision.

It doesn’t model water column (meters H₂O, feet H₂O) or mercury-column at non-standard temperatures. Both are specialist and rarely encountered outside specific industries. For the underlying force side, the weight converter covers the mass units that back pressure calculations.

Frequently asked questions

Are mmHg and torr the same thing?

Almost but not quite. Torr is defined as exactly 1/760 of a standard atmosphere (101325 / 760 Pa ≈ 133.32237 Pa), while millimetres of mercury is defined by the physics of a mercury column at 0 °C under standard gravity (133.322387415 Pa exactly). The difference shows up around the sixth decimal place — negligible for any practical use, but not zero. Medical blood pressure readings, chemistry vacuum work, and meteorological barometers all use 'mmHg' and 'torr' interchangeably in practice. This converter treats them as separate units because the math is slightly different at full precision.

Why is 'atm' exactly 101325 Pa?

Because it was defined that way in 1954 by the International Committee for Weights and Measures. Before the 1954 definition, one atmosphere meant 'typical sea-level pressure', which varies slightly by location, temperature, and weather. The 1954 CIPM resolution pinned it down to exactly 101,325 pascals, which matches the average sea-level pressure at 45° latitude and 0°C closely enough for practical use while being an exact value for scientific work.

Where is inHg used?

Almost entirely in US aviation and US home barometers. US weather reports quote barometric pressure in inches of mercury (typical range 29.7–30.2 inHg). Aircraft altimeters are calibrated against a reference pressure in inHg (Europe uses hPa). Outside these two contexts, inHg is essentially gone — medical blood pressure uses mmHg, weather worldwide uses hPa/mbar, engineering uses bar/kPa/psi.

What is MPa used for?

High-pressure industrial work. Hydraulic systems typically operate at 10–35 MPa (1,450–5,076 psi). Water jet cutting runs at 200–400 MPa. The ultimate tensile strength of structural steel is around 400–900 MPa. Concrete compressive strength is in the 20–80 MPa range. Anywhere you see 'bar' getting unwieldy (above about 100 bar = 10 MPa = 1,450 psi), engineers switch to MPa.

Which unit should I use?

Depends on the field: weather forecasts use hectopascals or inches of mercury; tire pressures use bar or psi; SCUBA tanks use bar or psi; laboratory chemistry and medicine use mmHg/torr; industrial hydraulics use MPa or bar; aviation altimeters use inHg or hPa. The general principle: pick the unit whose typical values are three or four significant digits in the situation you're measuring. Nobody wants to quote atmospheric pressure as '0.101 MPa' or tire pressure as '220000 Pa'.