Torr to Pascals Converter

Pressure is one of those quantities that almost every scientific and medical discipline needs to measure, yet the unit used varies wildly from one field to the next. Physicists write papers in pascals. Weather forecasters and vacuum engineers reach for millibar or torr. Aviation crews use inches of mercury on their altimeters. Medical blood-pressure cuffs are still calibrated in mmHg. Anesthesiologists read gas pressures in kPa on modern machines but legacy manometers on the wall behind them still say "mmHg." Every time you cross between two of these communities you have to convert, and the conversion factor, 1 torr = 133.322387415 pascals, exactly, is the bridge. This calculator does the bidirection conversion instantly, with bonus read-outs in bar, atm, kPa, psi and mbar so you never have to chase a second table.

How to Use

1. Type a pressure value into the Torr (mmHg) field on the left. The default is 760 torr, the standard atmosphere.
2. Read the matching pressure in pascals on the right; the field updates as you type.
3. Type a pressure in pascals instead if you want to convert in the opposite direction, the torr field updates immediately.
4. Click the ⇄ swap button to push the current pascal value into the torr field and vice versa.
5. Use the bonus read-outs (bar, atm, kPa, psi, mbar) below for the same pressure expressed in the other common units.
6. Click Copy torr or Copy Pa to copy the primary result to your clipboard for pasting into a lab notebook or spreadsheet.
7. Negative values are rejected at the input stage because absolute pressure in vacuum work is non-negative; for gauge pressure below one atmosphere subtract the local barometer reading first.
8. Use the bottom-of-page constant strip to confirm the exact conversion factor you are working with: 1 torr = 133.322387415 Pa, and 1 Pa = 7.50062 × 10⁻³ torr.

The Formulas

The conversions used by this calculator rest on three exact constants:

• 1 torr = 133.322387415 Pa (CIPM 1980, reaffirmed by CIPM 2007; adopted in ISO 80000-9:2009 §A.4 and tabulated in NIST SP 811 §B.8)
• 1 atm = 101 325 Pa exactly (CIPM; BIPM SI Brochure 9th ed. §2.3.3)
• 1 bar = 100 000 Pa exactly (BIPM SI Brochure §2.3.3)

By construction, 1 torr = 1/760 atm, because the torr was originally defined as the pressure exerted by a column of mercury exactly one millimetre tall under standard gravity, and there are 760 such columns in a standard atmosphere. The 133.322387415 figure is therefore not measured but defined: it is 101 325 / 760, evaluated to the full nine-figure precision that CIPM publishes. The formula is simply:

• P [Pa] = P [torr] × 133.322387415
• P [torr] = P [Pa] ÷ 133.322387415

From these two identities, every other unit on the bonus row falls out:

• bar: multiply by 133.322387415 / 100 000 = 0.00133322387415
• atm: multiply by 1 / 760 ≈ 1.31578947368421 × 10⁻³
• kPa: multiply by 0.133322387415
• psi: multiply by 133.322387415 / 6894.757293168 ≈ 0.0193367747
• mbar: multiply by 1.33322387415 (a millibar is 100 Pa; 100 / 133.322387415 gives the inverse path)

The CIPM 1980 definition replaced an older "1 torr = 1 mmHg" rule that strictly required the mercury to be at 0 °C under standard gravity (g = 9.806 65 m/s²). The newer convention fixes the numeric value of 1 torr as 133.322387415 Pa regardless of the fluid's actual temperature. For 99.99 % of laboratory work the distinction is invisible: at 20 °C mercury density drops by about 0.17 %, which is two orders of magnitude smaller than the precision of a typical analog gauge.

Worked Examples

Example 1, Standard atmosphere. 760 torr × 133.322387415 Pa/torr = 101 325 Pa exactly. That is the whole reason the torr is defined as 1/760 atm, multiplying 760 by the canonical constant returns the canonical atmosphere to full precision. In bar this is 1.01325 bar (since 1 atm = 101 325 Pa and 1 bar = 100 000 Pa), in atm it is 1.0000000, in kPa it is 101.325, and in psi it is 14.69594878.

Example 2, One torr in pascals. 1 torr = 133.322387415 Pa exactly. That is 0.00131578947 atm, 0.00133322387 bar, 0.13332238742 kPa, 0.01933677470 psi, and 1.33322387415 mbar. It is also roughly the pressure reduction of the Earth's atmosphere for every 105 metres you climb, which is why a typical lab rough vacuum of 10⁻³ torr is so low that you can no longer use it to push air around.

Example 3, A rotary-vane pump. A standard two-stage rotary-vane pump pulls a foreline down to about 10⁻³ torr = 1.33 × 10⁻¹ Pa, or 0.00133 mbar. A turbomolecular pump stacked on top then drags the chamber into the high-vacuum regime of 10⁻⁷ torr = 1.33 × 10⁻⁵ Pa. In psi the same range is 10⁻⁹ to 10⁻⁵ psi, which is why vacuum workers almost never quote psi at the chamber, the numbers become silly.

Example 4, Anesthesia machine gas pressure. Modern anesthesia machines deliver oxygen at a wall-outlet pressure around 50 psi (≈ 3.4 bar, ≈ 345 kPa, ≈ 2588 torr). That is four times the partial pressure of O₂ at sea level. Vaporisers drop the volatile-agent pressure to a partial pressure of a few kPa before mixing with the carrier gas. The conversion 2588 torr × 133.322387415 ≈ 345 000 Pa lets the machine's sensors report in the SI units used internally.

Example 5, Blood pressure. A healthy systolic reading of 120 mmHg (120 torr by the equivalence) is 120 × 133.322387415 ≈ 15 998.7 Pa, or about 16 kPa. Diastolic 80 mmHg = 80 × 133.322387415 ≈ 10 665.8 Pa ≈ 10.7 kPa. Mean arterial pressure is roughly 93 mmHg ≈ 12.4 kPa. These are the numbers you see on intra-arterial line traces in ICU; the cuff reading on the ward is still in mmHg for historical reasons, and the conversion back and forth is exactly what this calculator does.

Where It Shows Up

• Vacuum science, every chamber pressure from rough (10⁻³ torr) to UHV (< 10⁻⁹ torr) is quoted in torr or Pa interchangeably; pump-down curves plot both.
• Barometry and altimetry, mercury barometers measure atmospheric pressure directly in mmHg, which is then converted to Pa or hPa for meteorological reports and aircraft altimeters.
• Anesthesia machines, pipeline pressures and ventilator gauge pressures are read in kPa or cmH₂O but the manometer blocks on the wall often still display mmHg.
• Gas laws and ideal-gas calculations, PV = nRT requires absolute pressure in Pa; any starting value in torr or mmHg must first be converted.
• Mass spectrometry, ion-source and analyser pressures are quoted in torr (or sometimes mbar) because the relevant gas-flow regime (molecular vs. viscous) lives in those orders of magnitude.
• Blood pressure measurement, the cuff reading is mmHg; the gold-standard intra-arterial transducer reports mmHg or kPa. Conversion between the two is a daily task in cardiology and critical care.
• Semiconductor fabrication, process-chamber base pressure, load-lock pressure, and tool-particles-per-million leak-rate specifications all hinge on a clean, traceable conversion between torr and Pa (and the related units sccm and mTorr·L/s).

Common Mistakes

• Treating torr and mmHg as exactly the same at non-zero temperature. They are defined to be numerically identical (1 torr = 1 mmHg by CIPM), but the strict mmHg depends on the density of mercury at 0 °C, whereas the CIPM torr fixes the numeric value in pascals regardless of fluid temperature. At 20 °C the gap is about 0.017 %, usually invisible, occasionally meaningful in traceable calibration.
• Converting via atm when you don't need to. Some textbooks teach "torr → atm → Pa" using 1 atm = 760 torr and 1 atm = 101 325 Pa. The intermediate atm step adds rounding unless you keep full precision. The direct factor 1 torr = 133.322387415 Pa (CIPM, exact) avoids the detour entirely.
• Rounding 133.322 to 133.3 in your head. A 0.02 % error per torr is harmless for weather forecasting but unacceptable for vacuum gauge calibration or leak-rate testing. Use the full factor.
• Forgetting that gauge and absolute pressure are different. A barometer at the foot of a mountain reads ~760 torr absolute; an HVAC technician's gauge on a pump reads -0.5 bar gauge (which is 0.5 bar absolute, or ~380 torr). The converter does not know which regime you are in, you do. Subtract atmospheric first if you have a gauge reading and want absolute.

Frequently Asked Questions

What is the exact relationship between torr and pascals?

1 torr = 133.322387415 Pa exactly, as defined by the Comité International des Poids et Mesures (CIPM 1980, reaffirmed 2007) and adopted in ISO 80000-9:2009. The figure is not measured: it is computed as 101 325 Pa / 760, and the CIPM has frozen the numeric value to nine significant figures for the foreseeable future.

Is torr the same as mmHg?

Numerically, yes, 1 torr = 1 mmHg by definition. Historically "mmHg" referred to the pressure exerted by a 1 mm column of mercury at 0 °C under standard gravity, while "torr" was introduced in 1954 as a name for the same unit that did not reference a physical substance. The CIPM 1980 reconciliation fixed the numeric value of 1 torr as 133.322387415 Pa regardless of fluid temperature, so the distinction is now purely semantic.

How do I convert 760 torr to pascals?

Multiply 760 by 133.322387415 to get 101 325 Pa exactly. This is the standard atmosphere. For 1 torr the result is 133.322387415 Pa; for 1 kPa the result is 7.50061683 torr. The calculator handles all of these directions instantly.

Why do vacuum gauges still show torr instead of pascals?

Torr (and its cousin mTorr) is the working language of vacuum science because the typical chamber pressures, 10⁻⁹ to 10³, span many orders of magnitude, and the torr is conveniently close to 1 mmHg, the unit that older mercury manometers naturally read. Pa is preferred in SI textbooks and academic papers, but in the lab the gauge head often says "torr" because that is what the calibration certificate traces back to.

How does this relate to bar and atm?

1 bar = 100 000 Pa exactly and 1 atm = 101 325 Pa exactly, so 1 bar ≈ 0.986923 atm ≈ 750.0616 torr. Weather reports use bar (or mbar, which is 1/1000 of a bar); laboratory gas laws use atm or Pa; vacuum work uses torr. The bonus read-outs on the calculator give all of these from a single input so you never have to chain conversions.

What about blood pressure, is that torr or mmHg?

By long-standing clinical convention blood pressure is measured in mmHg. 120/80 mmHg therefore means 120 torr and 80 torr, about 15 999 Pa and 10 666 Pa respectively. If your hospital charting system records in kPa, multiply the mmHg value by 0.133322 to convert. Mean arterial pressure (the physiologically meaningful average) is approximately 93 mmHg, or about 12.4 kPa.

This converter is intended for professional and educational use in vacuum science, chemistry, medicine, metrology and engineering. The conversion factors implemented here follow the CIPM 1980/2007 decisions, ISO 80000-9:2009 and the NIST SP 811 (2008) guidance. We refresh the constants whenever NIST, BIPM or CIPM publishes a revision that affects the torr-pascal relationship; the displayed factor strip at the bottom of the tool reflects the current values.

References

• NIST SP 811 (2008). Guide for the Use of the International System of Units (SI). §B.8, Non-SI units accepted for use with the SI (torr, mmHg, bar, atm). For the Torr To Pa, National Institute of Standards and Technology.
• CIPM (1980, reaffirmed 2007). Recommandation 1 (CI-1980): Value of the torr. Comité International des Poids et Mesures, Procès-Verbaux.
• ISO 80000-9:2009. Quantities and units, Part 9: Physical chemistry and molecular physics. Annex A, The torr. International Organization for Standardization.
• IUPAC (2007). Quantities, Units and Symbols in Physical Chemistry (the "Green Book"). 3rd ed., RSC Publishing. §2.3, Pressure units (torr, bar, atm, Pa).
• BIPM (2019). The International System of Units (SI Brochure). 9th ed., §2.3.3, Non-SI units (bar, atm) and the pascal as the SI pressure unit. For the Torr To Pa, Bureau International des Poids et Mesures, Sèvres.