psi to mmHg Converter
1 psi = 51.7149 mmHg (conventional millimeters of mercury). Since 1 standard atmosphere = 14.69595 psi = 760 mmHg, 1 psi = 760 / 14.69595 = 51.7149 mmHg. This conversion is used...
Formula
Source: NIST SP 811, ISO 80000-4 | Last reviewed: June 27, 2026
Examples
1 psi
= 51.71 mm Hg
1 psi = 51.71 mmHg
14.696 psi
= 760 mm Hg
14.696 psi = 760 mmHg (standard atmosphere)
2.32 psi
= 120 mm Hg
2.32 psi = 120 mmHg (typical systolic blood pressure)
30 psi
= 1551 mm Hg
30 psi = 1,551 mmHg (≈ 2 atm)
Quick Reference Table
| psi | mmHg | Context |
|---|---|---|
| 1 | 51.7 | Small pressure increment |
| 2.32 | 120 | Normal systolic blood pressure |
| 14.696 | 760 | Standard atmospheric pressure |
| 30 | 1551 | ~2 atm (compressed air) |
| 100 | 5171 | ~7 atm (industrial compressed air) |
| 1000 | 51715 | ~68 atm (high-pressure) |
Where is this used?
Since 1 standard atmosphere = 14.69595 psi = 760 mmHg, 1 psi = 760 / 14.69595 = 51.7149 mmHg.
This is essentially the same conversion as psi-to-torr, because mmHg and torr are identical for all practical engineering purposes (differing by less than 0.000015%).
The mmHg (millimeter of mercury) is the traditional unit for barometric pressure (weather reports, altimeter settings), blood pressure measurement (systolic/diastolic: 120/80 mmHg), and vacuum measurement in laboratories and medical settings.
The relationship 760 mmHg = 14.7 psi is as fundamental as 2.54 cm = 1 inch, it's the absolute reference point for converting between US customary and mercury-column pressure units.
A US industrial pressure gauge reading 30 psi corresponds to 30 × 51.715 = 1,551 mmHg, about 2 atmospheres.
Conversely, the human systolic blood pressure of 120 mmHg is only 120 / 51.715 = 2.32 psi, illustrating why mercury columns are used for the low-pressure ranges in medical and barometric measurements: a 2 psi pressure is difficult to read accurately on a Bourdon tube gauge but is easily observed as a 120 mm column height.
In vacuum engineering, a rough vacuum of 25 inHg (inches of mercury, where 1 inHg = 25.4 mmHg) is 635 mmHg, equivalent to 12.28 psi absolute (or −2.42 psig at sea level).
A US vacuum gauge reading 25 inHg vacuum converts to 635 mmHg, a unit more commonly used in European vacuum equipment specifications.
The relationship between psi and mmHg is linear and fixed by the density of mercury (13.5951 g/cm³ at 0°C) and standard gravity (9.80665 m/s²), but the commonly used conversion factor 1 psi = 51.715 mmHg uses the standard atmosphere definition rather than the physical mercury density, making it a defined (exact) rather than measured value.
For any engineering calculation where pressure is used in force/area equations (stress, pipe wall thickness, flange rating), convert mmHg to psi first, the mercury column units are calibration references, not force units.
Real-World Usage Scenarios
Medical device pressure calibration
A US medical device manufacturer produces an anesthesia machine for global markets. The machine's oxygen pressure regulator is calibrated to deliver 50 psig (3.45 barg) to the flowmeters, but the pressure gauge on the regulator is in mmHg (for medical convention). The conversion: 50 × 51.715 = 2,586 mmHg. The pressure regulator is calibrated to 2,586 ± 50 mmHg (the ±2% tolerance per FDA performance standards). The conversion from psi to mmHg is applied at every calibration step. For the European market (where bar is standard), the regulator is also calibrated to 3.45 ± 0.07 bar. The psi-to-mmHg conversion (× 51.715) and psi-to-bar conversion (× 0.06895) both produce the same physical pressure, but the calibration report uses the local unit. A 1% error in the psi-to-mmHg conversion corresponds to about 26 mmHg, which is above the calibration tolerance, the regulator would fail the calibration test. The conversion must be exact for medical device compliance.
Industry Standards Referenced
Frequently Asked Questions
Are mmHg and Torr the same?
For all practical engineering work, yes. 760 mmHg = 760 Torr = 1 standard atmosphere = 14.69595 psi. The minute theoretical difference (about 0.000015%) arises from whether you define the unit by the density of mercury at 0°C (mmHg) or by the fraction of a standard atmosphere (Torr, exactly 1/760 atm). This difference is smaller than the accuracy of any commercially available pressure gauge.
What's the relationship between psi and mmHg in vacuum measurement?
At standard atmospheric pressure, 14.696 psi = 760 mmHg. A vacuum gauge reading 25 inHg (635 mmHg) below atmospheric indicates an absolute pressure of 125 mmHg = 2.42 psia = -12.28 psig (at sea level). The psi-to-mmHg conversion is applied at every vacuum specification.
Can I use this conversion for medical pressure measurements?
Yes. Blood pressure is typically reported in mmHg (e.g., 120/80 mmHg systolic/diastolic). Converting: 120 mmHg = 120 × 0.01934 = 2.32 psi, 80 mmHg = 1.55 psi. The conversion is useful for medical device calibration in dual-unit instruments (e.g., anesthesia machine pressure gauges).
Reviewed for accuracy
Verified against NIST pressure conversion standards · Last reviewed: June 27, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.