Calculator
Vacuum and pressure unit converter: mbar, Torr, Pa, micron, psi
1 mbar is 100 Pa or 0.750062 Torr. The converter turns any pressure into 16 units at once – from mbar and Pa to Torr, micron, psi and inHg, as absolute and as gauge pressure – and shows which ISO 3529-1 vacuum range the value falls in.
- 16pressure and vacuum units
- 133.322 Paequal 1 Torr
- 1,013.25 hPaISO 2533 standard atmosphere
- 5vacuum ranges in ISO 3529-1
The converter needs JavaScript. The conversion tables further down work without it.
Absolute pressure
Gauge pressure
Vacuum relative to ambient pressure
Vacuum range
Ambient pressure used:
| Unit | absolute | gauge |
|---|---|---|
| Millibar (mbar) | ||
| Hectopascal (hPa) | ||
| Pascal (Pa) | ||
| Kilopascal (kPa) | ||
| Megapascal (MPa) | ||
| Bar (bar) | ||
| Torr | ||
| Millitorr (mTorr) | ||
| Micron (µmHg) | ||
| Millimetre of mercury (mmHg) | ||
| Inch of mercury (inHg) | ||
| Pound per square inch (psi) | ||
| Standard atmosphere (atm) | ||
| Technical atmosphere (at, kgf/cm²) | ||
| Millimetre of water (mmH₂O) | ||
| Inch of water (inH₂O) |
Converting gauge pressure to absolute pressure
Absolute pressure is measured against the ideal vacuum (0 Pa), gauge pressure against the ambient pressure. The relation is:
pabs = pamb + pgauge
A vacuum therefore has a negative gauge pressure. Example: a vacuum gauge reads −0.8 bar. At an ambient pressure of 1,013.25 hPa, the absolute pressure is 1,013.25 mbar − 800 mbar = 213.25 mbar. Relative to ambient pressure, that is about 79% vacuum.
On this page, percentages mean: 0% vacuum is ambient pressure, 100% is 0 Pa absolute. Vacuum in % = (pamb − pabs) / pamb × 100%.
Ambient pressure depends on altitude and weather; ISO 3529-1 gives roughly 31 kPa (Mount Everest, low-pressure weather) to 110 kPa (Dead Sea, high-pressure weather) on the Earth’s surface. When you convert a gauge reading, enter the actual barometric pressure on site. If you leave the default, the converter uses 1,013.25 hPa, the sea-level pressure of the ISO 2533 standard atmosphere.
| Gauge pressure in bar | Gauge pressure in psi | Absolute pressure in mbar | Absolute pressure in Torr | Vacuum in % |
|---|---|---|---|---|
| 0 | 0 | 1,013.25 | 760 | 0 |
| −0.1 | −1.45038 | 913.25 | 684.994 | 9.87 |
| −0.2 | −2.90075 | 813.25 | 609.988 | 19.74 |
| −0.3 | −4.35113 | 713.25 | 534.981 | 29.61 |
| −0.4 | −5.80151 | 613.25 | 459.975 | 39.48 |
| −0.5 | −7.25189 | 513.25 | 384.969 | 49.35 |
| −0.6 | −8.70226 | 413.25 | 309.963 | 59.22 |
| −0.7 | −10.1526 | 313.25 | 234.957 | 69.08 |
| −0.8 | −11.603 | 213.25 | 159.951 | 78.95 |
| −0.9 | −13.0534 | 113.25 | 84.9445 | 88.82 |
| −0.95 | −13.7786 | 63.25 | 47.4414 | 93.76 |
| −0.99 | −14.3587 | 23.25 | 17.4389 | 97.71 |
| −1 | −14.5038 | 13.25 | 9.93832 | 98.69 |
So −1 bar gauge is not an absolute vacuum: at 1,013.25 hPa ambient pressure, 13.25 mbar absolute remain. 0 Pa absolute would be −1.01325 bar gauge.
Vacuum conversion chart
Common vacuum levels from standard atmosphere down to 10⁻⁹ mbar, rounded to six significant digits. All values are absolute pressures; psi means psia here. The range column assumes an ambient pressure of 1,013.25 hPa.
| mbar | Pa | Torr | Micron (µmHg) | psi (a) | ISO 3529-1 range |
|---|---|---|---|---|---|
| 1,013.25 | 101,325 | 760 | 760,000 | 14.6959 | Standard atmosphere |
| 1,000 | 100,000 | 750.062 | 750,062 | 14.5038 | Low (rough) vacuum |
| 800 | 80,000 | 600.049 | 600,049 | 11.603 | Low (rough) vacuum |
| 500 | 50,000 | 375.031 | 375,031 | 7.25189 | Low (rough) vacuum |
| 300 | 30,000 | 225.019 | 225,018 | 4.35113 | Low (rough) vacuum |
| 200 | 20,000 | 150.012 | 150,012 | 2.90075 | Low (rough) vacuum |
| 100 | 10,000 | 75.0062 | 75,006.2 | 1.45038 | Low (rough) vacuum |
| 50 | 5,000 | 37.5031 | 37,503.1 | 0.725189 | Low (rough) vacuum |
| 20 | 2,000 | 15.0012 | 15,001.2 | 0.290075 | Low (rough) vacuum |
| 10 | 1,000 | 7.50062 | 7,500.62 | 0.145038 | Low (rough) vacuum |
| 5 | 500 | 3.75031 | 3,750.31 | 0.0725189 | Low (rough) vacuum |
| 1 | 100 | 0.750062 | 750.062 | 0.0145038 | Low (rough) vacuum |
| 0.5 | 50 | 0.375031 | 375.031 | 7.25189 × 10⁻³ | Medium (fine) vacuum |
| 0.1 | 10 | 0.0750062 | 75.0062 | 1.45038 × 10⁻³ | Medium (fine) vacuum |
| 0.05 | 5 | 0.0375031 | 37.5031 | 7.25189 × 10⁻⁴ | Medium (fine) vacuum |
| 0.01 | 1 | 7.50062 × 10⁻³ | 7.50062 | 1.45038 × 10⁻⁴ | Medium (fine) vacuum |
| 5 × 10⁻³ | 0.5 | 3.75031 × 10⁻³ | 3.75031 | 7.25189 × 10⁻⁵ | Medium (fine) vacuum |
| 1 × 10⁻³ | 0.1 | 7.50062 × 10⁻⁴ | 0.750062 | 1.45038 × 10⁻⁵ | Medium (fine) vacuum |
| 1 × 10⁻⁴ | 0.01 | 7.50062 × 10⁻⁵ | 0.0750062 | 1.45038 × 10⁻⁶ | High vacuum |
| 1 × 10⁻⁵ | 1 × 10⁻³ | 7.50062 × 10⁻⁶ | 7.50062 × 10⁻³ | 1.45038 × 10⁻⁷ | High vacuum |
| 1 × 10⁻⁶ | 1 × 10⁻⁴ | 7.50062 × 10⁻⁷ | 7.50062 × 10⁻⁴ | 1.45038 × 10⁻⁸ | High vacuum |
| 1 × 10⁻⁷ | 1 × 10⁻⁵ | 7.50062 × 10⁻⁸ | 7.50062 × 10⁻⁵ | 1.45038 × 10⁻⁹ | High vacuum |
| 1 × 10⁻⁸ | 1 × 10⁻⁶ | 7.50062 × 10⁻⁹ | 7.50062 × 10⁻⁶ | 1.45038 × 10⁻¹⁰ | High vacuum |
| 1 × 10⁻⁹ | 1 × 10⁻⁷ | 7.50062 × 10⁻¹⁰ | 7.50062 × 10⁻⁷ | 1.45038 × 10⁻¹¹ | Ultra-high vacuum |
The Torr and micron columns can differ in the sixth digit (for example at 300 mbar) because 1 micron is defined as 10⁻³ mmHg, and 1 mmHg is larger than 1 Torr by about 1.4 × 10⁻⁷ of its value.
Vacuum ranges in ISO 3529-1
ISO 3529-1:2019 divides vacuum into five ranges. Vacuum starts below the prevailing ambient pressure. The standard calls the limits approximations; each limit value belongs to the range with the higher pressure. So 1 mbar (100 Pa) is still low vacuum, and 10⁻³ mbar (0.1 Pa) is still medium vacuum.
| Range | Pa | mbar | Torr (rounded) |
|---|---|---|---|
| Low (rough) vacuum | ambient pressure to 100 | to 1 | to 0.75 |
| Medium (fine) vacuum | below 100 to 0.1 | below 1 to 10⁻³ | to 7.5 × 10⁻⁴ |
| High vacuum (HV) | below 0.1 to 10⁻⁶ | below 10⁻³ to 10⁻⁸ | to 7.5 × 10⁻⁹ |
| Ultra-high vacuum (UHV) | below 10⁻⁶ to 10⁻⁹ | below 10⁻⁸ to 10⁻¹¹ | to 7.5 × 10⁻¹² |
| Extreme-high vacuum (XHV) | below 10⁻⁹ | below 10⁻¹¹ | below 7.5 × 10⁻¹² |
Comparison with the German classification
German reference works use the terms Grobvakuum, Feinvakuum, Hochvakuum and Ultrahochvakuum with slightly different limits. The German standard DIN 28400-1 (edition 1990-05, still current according to DIN) covers vacuum ranges in its first clause. The limits in the table are not taken from the standard itself but from two independent reference works that give them in agreement.
| Range | ISO 3529-1:2019 | German classification |
|---|---|---|
| Low (rough) vacuum / Grobvakuum | to 100 Pa | 10⁵ to 10² Pa |
| Medium (fine) vacuum / Feinvakuum | 100 to 0.1 Pa | 10² to 10⁻¹ Pa |
| High vacuum / Hochvakuum | 0.1 to 10⁻⁶ Pa | 10⁻¹ to 10⁻⁵ Pa |
| Ultra-high vacuum / Ultrahochvakuum | 10⁻⁶ to 10⁻⁹ Pa | below 10⁻⁵ Pa |
| Extreme-high vacuum | below 10⁻⁹ Pa | not consistent in the sources |
The main difference: in ISO 3529-1:2019, high vacuum extends to 10⁻⁶ Pa (10⁻⁸ mbar); in the German classification it ends at 10⁻⁵ Pa (10⁻⁷ mbar). A pressure of 10⁻⁸ mbar is therefore still high vacuum under ISO but already Ultrahochvakuum in the German classification.
Conversion factors and definitions
Every factor rests on a definition. The converter calculates at full precision and only rounds the display. An ellipsis (…) marks values with infinitely many decimal places.
| Unit | 1 unit in Pa | 1 mbar in the unit | Definition |
|---|---|---|---|
| Millibar (mbar) | 100 | 1 | 1 mbar = 10⁻³ bar = 100 Pa |
| Hectopascal (hPa) | 100 | 1 | 1 hPa = 100 Pa = 1 mbar |
| Pascal (Pa) | 1 | 100 | SI unit: 1 Pa = 1 N/m² |
| Kilopascal (kPa) | 1,000 | 0.1 | 1 kPa = 1,000 Pa |
| Megapascal (MPa) | 1,000,000 | 1 × 10⁻⁴ | 1 MPa = 10⁶ Pa |
| Bar (bar) | 100,000 | 1 × 10⁻³ | 1 bar = 10⁵ Pa (exact) |
| Torr | 133.322368421… | 0.750062 | 1 Torr = 101,325/760 Pa (exact) |
| Millitorr (mTorr) | 0.133322368421… | 750.062 | 1 mTorr = 10⁻³ Torr |
| Micron (µmHg) | 0.133322387415 | 750.062 | 1 micron = 10⁻³ mmHg; treated as 1 mTorr in vacuum practice |
| Millimetre of mercury (mmHg) | 133.322387415 | 0.750062 | conventional: 13.5951 g/cm³ × 9.80665 m/s² × 1 mm |
| Inch of mercury (inHg) | 3,386.388640341 | 0.02953 | conventional: 25.4 mmHg |
| Pound per square inch (psi) | 6,894.757293168… | 0.0145038 | 1 lbf/in² with 1 lb = 0.45359237 kg, 1 in = 0.0254 m, gₙ = 9.80665 m/s² |
| Standard atmosphere (atm) | 101,325 | 9.86923 × 10⁻⁴ | 1 atm = 101,325 Pa (exact) |
| Technical atmosphere (at, kgf/cm²) | 98,066.5 | 1.01972 × 10⁻³ | 1 at = 1 kgf/cm² = 98,066.5 Pa (exact) |
| Millimetre of water (mmH₂O) | 9.80665 | 10.1972 | conventional: 1,000 kg/m³ × 9.80665 m/s² × 1 mm |
| Inch of water (inH₂O) | 249.08891 | 0.401463 | conventional: 25.4 mmH₂O |
Torr and mmHg are not quite the same
1 Torr is defined as 101,325/760 Pa, that is 133.322368421… Pa. The conventional millimetre of mercury is based on a mercury density of 13.5951 g/cm³ and standard gravity of 9.80665 m/s² and equals 133.322387415 Pa. The two values agree in their first seven digits (133.3223…) and differ from the eighth digit on: by about 1.9 × 10⁻⁵ Pa, or 1.4 × 10⁻⁷ of the value. This only matters in metrology; for the same reason, 1 micron is taken as 1 mTorr in practice.
Variants with a reference temperature
Besides the conventional values, there are mercury and water column units tied to a temperature. NIST SP 811 lists, for example: inHg at 32 °F 3,386.38 Pa, inHg at 60 °F 3,376.85 Pa, inH₂O at 39.2 °F (4 °C) 249.082 Pa and inH₂O at 60 °F 248.84 Pa. The converter uses the conventional values, 3,386.388640341 Pa for 1 inHg and 249.08891 Pa for 1 inH₂O.
Vacuum pumps and vacuum ranges
For low and medium vacuum, ISO 3529-1 names positive displacement vacuum pumps; for high vacuum and lower pressures it names high vacuum pumps. Ehrler & Beck sells and services vacuum pumps of the following designs. Their ultimate pressures and pumping speeds are listed on the technology pages:
Sources
All factors and limits on this page come from the documents below. The converter calculates with the exact definitions and rounds the display to six significant digits.
- NIST Special Publication 811 (2008), Guide for the Use of the International System of Units, Appendix B.8/B.9 (conversion factors, footnotes 8, 12, 22, 23)
- BIPM, 10th CGPM (1954), Resolution 4 (standard atmosphere 101,325 Pa)
- BIPM, 3rd CGPM (1901), Declaration 2 (standard acceleration of free fall 9.80665 m/s²)
- IUPAC, Quantities, Units and Symbols in Physical Chemistry (Green Book), 3rd ed., 2nd printing 2012, section 7.2, p. 138 (torr and conventional mmHg)
- WMO Codes Registry, millimetre of mercury (133.322387415 Pa)
- ISO 3529-1:2019, Vacuum technology – Vocabulary – Part 1: General terms (clauses 3.1.1 and 3.1.2)
- K. Jousten (PTB): ISO standards for vacuum metrology, 7th CCM and IMEKO TC-16 Conference, 2023 (Table 2: vacuum ranges of ISO 3529-1:2019)
- ISO 2533:1975, Standard Atmosphere (Table 1: sea-level pressure 101,325 Pa)
- DIN 28400-1:1990-05, Vakuumtechnik; Benennung und Definitionen; Allgemeine Benennungen (current according to DIN; clause 1 covers vacuum ranges; standard text not consulted)
- German classification, two independent sources: Lexikon der Chemie, “Vakuum”, Spektrum Akademischer Verlag, 1998; A. Winkler, TU Graz: Vakuumphysik und Vakuumtechnologie
Questions
Frequently asked questions
How do I convert gauge pressure to absolute pressure?
Add the gauge pressure to the ambient pressure: absolute pressure = ambient pressure + gauge pressure. At 1,013.25 hPa ambient pressure, −0.8 bar gauge gives 213.25 mbar absolute.
How many Torr is 1 mbar?
1 mbar is 0.750062 Torr, and 1 Torr is 1.33322 mbar. The standard atmosphere of 1,013.25 mbar is exactly 760 Torr.
What is a micron in vacuum measurement?
A micron is a micrometre of mercury (µmHg), one thousandth of a mmHg or 0.133322 Pa. In vacuum practice, 1 micron is taken as 1 mTorr, so 1 Torr equals 1,000 microns.
Are Torr and mmHg the same?
Almost: 1 Torr is 101,325/760 Pa (133.322368 Pa), and 1 conventional mmHg is 133.322387 Pa. The relative difference of about 1.4 × 10⁻⁷ only matters in metrology.
What are the vacuum ranges?
ISO 3529-1:2019 distinguishes low (rough) vacuum down to 100 Pa (1 mbar), medium vacuum to 0.1 Pa, high vacuum to 10⁻⁶ Pa, ultra-high vacuum to 10⁻⁹ Pa and extreme-high vacuum below that. The standard calls these limits approximations.
What does 99% vacuum mean?
The absolute pressure is still 1% of the ambient pressure. At 1,013.25 hPa ambient pressure, that is 10.1325 mbar absolute.
Is −1 bar a perfect vacuum?
No. At 1,013.25 hPa ambient pressure, −1 bar gauge still leaves 13.25 mbar absolute; 0 Pa absolute would be −1.01325 bar gauge.
Which ambient pressure should I enter?
The actual barometric pressure where you measure. Check whether a stated air pressure has been reduced to sea level: at higher altitudes the actual pressure is lower. If you enter nothing else, the converter uses 1,013.25 hPa.
Which vacuum pump suits your process?
We advise on vacuum pumps from many manufacturers and supply pumps, spare parts and service.
