Pressure unit conversion table
The table lists each supported unit with its value in pascals and its equivalent in the other common units.
| Unit | Pascals | In bar | In psi |
|---|---|---|---|
| 1 bar | 100,000 | 1 | 14.504 |
| 1 psi | 6,894.757 | 0.06895 | 1 |
| 1 kPa | 1,000 | 0.01 | 0.14504 |
| 1 atm | 101,325 | 1.01325 | 14.696 |
| 1 mmHg | 133.3224 | 0.001333 | 0.019337 |
- The mmHg factor (133.3224 Pa) is the conventional engineering value; the torr, defined as exactly 1/760 atm, differs from the mmHg by less than one part in seven million — negligible in practice.
- Most everyday pressure readings (tires, pipelines, compressors) are gauge pressures, measured relative to the surrounding atmosphere; add about 101.325 kPa to convert a gauge reading to absolute pressure.
- Actual atmospheric pressure varies with weather and altitude; the standard atmosphere is a fixed reference value, not the live barometric reading.
What are the common pressure units?
Pressure is force per unit area; the SI unit is the pascal (Pa), one newton per square metre. Because a pascal is tiny at everyday scales, practical work uses larger units: the kilopascal (1,000 Pa) and the bar, defined as exactly 100,000 Pa — conveniently close to atmospheric pressure at sea level. The bar is accepted for use alongside SI units.
The standard atmosphere (atm) is defined as exactly 101,325 Pa, a conventional reference value close to mean sea-level atmospheric pressure. The pound-force per square inch (psi) is the customary pressure unit in the United States, equal to 6,894.757 Pa; car tire pressures, for example, are commonly quoted around 32 psi, which is about 2.2 bar.
The millimetre of mercury (mmHg) descends from mercury-column barometers: it is the pressure exerted by a 1 mm column of mercury under standard conditions, conventionally 133.3224 Pa. It remains the standard unit for blood pressure in medicine and for vacuum work, where the essentially identical unit torr (defined as exactly 1/760 atm) is also used.
How to use this pressure converter
- Enter the pressure value you want to convert.
- Select its unit: bar, psi, kPa, atm or mmHg.
- Read the equivalent value in all five units simultaneously.
- For gauge readings, remember most instruments show pressure relative to the atmosphere; absolute pressure is the gauge value plus about 1 atm.
The conversion factors behind the pressure converter
The value is first converted to pascals using its unit's defined factor, then divided by each target unit's factor. The factors are standard definitions: 1 bar = 100,000 Pa (exact), 1 atm = 101,325 Pa (exact), 1 kPa = 1,000 Pa (exact), 1 psi = 6,894.757 Pa, 1 mmHg = 133.3224 Pa (conventional value).
Worked example: 2.5 bar = 250,000 Pa. In psi: 250,000 ÷ 6,894.757 = 36.26 psi. In kPa: 250 kPa. In atmospheres: 250,000 ÷ 101,325 = 2.467 atm. In mmHg: 250,000 ÷ 133.3224 = 1,875.2 mmHg.
Common mistakes
- Confusing gauge and absolute pressure: a tire at '32 psi' is 32 psi above atmospheric, roughly 46.7 psi absolute.
- Treating 1 bar and 1 atm as identical — they differ by 1.325%: 1 atm = 1.01325 bar.
- Mixing up mmHg and cmHg or inHg: blood pressure uses mmHg, aviation altimeters commonly use inHg (1 inHg = 25.4 mmHg = 3,386.39 Pa).
- Assuming psi values are metric-compatible without converting — hydraulic and pneumatic specs mix bar and psi frequently, and a 14.5× error means reading one as the other.
Часто задаваемые вопросы
How many psi is 1 bar?
1 bar equals 14.504 psi. The conversion follows from the definitions: 1 bar = 100,000 Pa and 1 psi = 6,894.757 Pa, so 100,000 ÷ 6,894.757 = 14.5038. For quick mental conversion, multiply bar by 14.5.
Is 1 bar the same as 1 atmosphere?
No, they are close but distinct. 1 bar is defined as exactly 100,000 Pa, while 1 standard atmosphere is defined as exactly 101,325 Pa. One atmosphere therefore equals 1.01325 bar — a 1.3% difference that matters in scientific and process work even though everyday usage often rounds them together.
Why is blood pressure measured in mmHg?
Early sphygmomanometers used an actual column of mercury, and the reading was literally the column height in millimetres. The unit persisted after mercury instruments were replaced: a blood pressure of 120/80 mmHg corresponds to about 16.0/10.7 kPa. One mmHg equals 133.3224 Pa by convention.
What is the difference between kPa and bar?
Both are metric pressure units based on the pascal: 1 bar = 100 kPa exactly. Kilopascals are the SI-preferred unit and appear in scientific work and some tire-pressure labels (a typical car tire is about 220 kPa); the bar remains popular in industry because 1 bar is close to atmospheric pressure.
What is the difference between mmHg and torr?
They are practically interchangeable. The torr is defined as exactly 1/760 of a standard atmosphere (101,325 ÷ 760 ≈ 133.3224 Pa), while the conventional millimetre of mercury is defined via the mercury column as 133.3224 Pa. The two differ by less than one part in seven million, far below any practical measurement precision.
Источники
- Bureau International des Poids et Mesures (BIPM). The International System of Units (SI Brochure), 9th edition, 2019 — the pascal and non-SI units accepted for use (bar, mmHg).
- NIST Special Publication 811 (Thompson & Taylor). Guide for the Use of the International System of Units (SI), 2008 — Appendix B pressure conversion factors.