Convert Inches of Mercury to Millimeters of Mercury
Instantly convert Inches of Mercury (inHg) to Millimeters of Mercury (mmHg) with our free online calculator.
Formula: inHg to mmHg — multiply by 25.4001
Reference Table
| Inches of Mercury (inHg) | Millimeters of Mercury (mmHg) |
|---|---|
| 1 | 25.4001 |
| 5 | 127 |
| 10 | 254.001 |
| 25 | 635.002 |
| 50 | 1270 |
| 100 | 2540.01 |
How to Convert Inches of Mercury to Millimeters of Mercury
Formula
To convert Inches of Mercury (inHg) to Millimeters of Mercury (mmHg): multiply by 25.4001
Step-by-Step
- Start with your value in Inches of Mercury (inHg).
- Multiply by 25.4001 to perform the conversion.
- The result is your value expressed in Millimeters of Mercury (mmHg).
Conversion Factor
1 inHg = 25.4001 mmHg
Reverse Factor
1 mmHg = 0.0393699 inHg
Worked Example
Convert 25 Inches of Mercury to Millimeters of Mercury: 25 inHg = 635.002 mmHg
About Inch of Mercury (inHg)
A pressure unit defined as the pressure exerted by a 1-inch column of mercury at the standard density of mercury (0 °C) and the standard acceleration of gravity (≈ 3,386.389 Pa per NIST SP 811). Inches of mercury are the primary unit in US aviation for altimeter settings (the QNH datum is reported in inHg in METAR weather observations — "Altimeter 30.12 inHg" means 30.12 inHg corrected to mean sea level), US barometric weather reporting on consumer indoor weather stations and TV weather graphics, HVAC and refrigeration duct/return static pressure (often quoted as fractions of an inHg, e.g., 0.25 inHg = ~62 Pa), and some legacy automotive vacuum gauges measuring intake-manifold vacuum below atmospheric (a healthy engine reads ~18-22 inHg of vacuum at idle). Standard sea-level atmospheric pressure is 29.92 inHg = 1013.25 hPa = 101.325 kPa.
About Millimeters of Mercury (mmHg)
A unit of pressure historically defined as the pressure exerted by a column of mercury exactly 1 millimeter tall at the standard acceleration of gravity (9.80665 m/s²) and the standard density of mercury (13,595.1 kg/m³ at 0 °C). The mmHg's contemporary definition rounds to exactly 133.322387415 Pa (NIST SP 811). Despite being non-SI, mmHg remains the international clinical standard for blood pressure measurement ("120 over 80" mmHg) per WHO and ESH guidelines, and is the default unit for intraocular pressure in ophthalmology (normal IOP 10-21 mmHg per Glaucoma Research Foundation) and intracranial pressure monitoring in neurology. Numerically the mmHg is almost identical to the torr (1 mmHg ≈ 1.0000007 torr — the difference is whether one uses the conventional density or the experimentally measured density of mercury). Barometric atmospheric pressure was historically quoted in mmHg before kPa/hPa adoption (760 mmHg = 1 atm = 101.325 kPa).
Quick Facts
- 1 Inch of Mercury equals 25.4001 Millimeters of Mercury
- 1 Millimeters of Mercury equals 0.0393699 Inches of Mercury
- Inch of Mercury is a unit of pressure
- Millimeters of Mercury is a unit of pressure
- This conversion is commonly used in tire inflation, weather reporting, scuba diving, and engineering
- The Inch of Mercury belongs to the imperial system
- The Millimeters of Mercury belongs to the metric system
Common Inch of Mercury to Millimeters of Mercury Conversions
| Inches of Mercury (inHg) | Millimeters of Mercury (mmHg) |
|---|---|
| 0.1 | 2.54001 |
| 0.5 | 12.7 |
| 1 | 25.4001 |
| 2 | 50.8002 |
| 5 | 127 |
| 10 | 254.001 |
| 14.696 | 373.28 |
| 15 | 381.001 |
| 20 | 508.002 |
| 25 | 635.002 |
| 50 | 1270 |
| 100 | 2540.01 |
| 150 | 3810.01 |
| 200 | 5080.02 |
| 500 | 12700 |
| 1000 | 25400.1 |
Understanding Inches of Mercury
The Inch of Mercury (symbol: inHg) is a unit of pressure. A pressure unit defined as the pressure exerted by a 1-inch column of mercury at the standard density of mercury (0 °C) and the standard acceleration of gravity (≈ 3,386.389 Pa per NIST SP 811). Inches of mercury are the primary unit in US aviation for altimeter settings (the QNH datum is reported in inHg in METAR weather observations — "Altimeter 30.12 inHg" means 30.12 inHg corrected to mean sea level), US barometric weather reporting on consumer indoor weather stations and TV weather graphics, HVAC and refrigeration duct/return static pressure (often quoted as fractions of an inHg, e.g., 0.25 inHg = ~62 Pa), and some legacy automotive vacuum gauges measuring intake-manifold vacuum below atmospheric (a healthy engine reads ~18-22 inHg of vacuum at idle). Standard sea-level atmospheric pressure is 29.92 inHg = 1013.25 hPa = 101.325 kPa.
It belongs to the imperial measurement system.
Inches of Mercury are commonly used in tire inflation, weather reporting, scuba diving, and engineering.
Understanding Millimeters of Mercury
The Millimeters of Mercury (symbol: mmHg) is a unit of pressure. A unit of pressure historically defined as the pressure exerted by a column of mercury exactly 1 millimeter tall at the standard acceleration of gravity (9.80665 m/s²) and the standard density of mercury (13,595.1 kg/m³ at 0 °C). The mmHg's contemporary definition rounds to exactly 133.322387415 Pa (NIST SP 811). Despite being non-SI, mmHg remains the international clinical standard for blood pressure measurement ("120 over 80" mmHg) per WHO and ESH guidelines, and is the default unit for intraocular pressure in ophthalmology (normal IOP 10-21 mmHg per Glaucoma Research Foundation) and intracranial pressure monitoring in neurology. Numerically the mmHg is almost identical to the torr (1 mmHg ≈ 1.0000007 torr — the difference is whether one uses the conventional density or the experimentally measured density of mercury). Barometric atmospheric pressure was historically quoted in mmHg before kPa/hPa adoption (760 mmHg = 1 atm = 101.325 kPa).
It belongs to the metric measurement system.
Millimeters of Mercury are commonly used in tire inflation, weather reporting, scuba diving, and engineering.
Why Convert Inches of Mercury to Millimeters of Mercury?
Engineers, mechanics, and scientists frequently need to convert pressure between Inches of Mercury and Millimeters of Mercury when working with different measurement standards. Tire pressure, blood pressure readings, weather barometric measurements, and industrial process specifications may all use different pressure units depending on the region or discipline. Reliable conversion prevents equipment misuse and ensures safety.
Frequently Asked Questions
How do I convert Inches of Mercury to Millimeters of Mercury?
A pressure unit defined as the pressure exerted by a 1-inch column of mercury at the standard density of mercury (0 °C) and the standard acceleration of gravity (≈ 3,386. To convert Inches of Mercury to Millimeters of Mercury, multiply by 25.4001. For example, 25 inHg equals 635.002 mmHg.
How many Millimeters of Mercury are in 1 Inch of Mercury?
There are 25.4001 Millimeters of Mercury in 1 Inch of Mercury.
How many Inches of Mercury are in 1 Millimeters of Mercury?
There are 0.0393699 Inches of Mercury in 1 Millimeters of Mercury.
What is the formula for Inch of Mercury to Millimeters of Mercury conversion?
The formula is: multiply by 25.4001. This means 1 inHg = 25.4001 mmHg.
Is a Inch of Mercury bigger than a Millimeters of Mercury?
No. One Inch of Mercury is smaller than one Millimeters of Mercury because 1 inHg equals 25.4001 mmHg, which is greater than 1.
When do you need to convert between Inches of Mercury and Millimeters of Mercury?
A unit of pressure historically defined as the pressure exerted by a column of mercury exactly 1 millimeter tall at the standard acceleration of gravity (9. Inch of Mercury and Millimeters of Mercury are both pressure units, so conversion comes up whenever one source of information uses one unit and another uses the other — a classic cross-reference challenge in engineering, trade, travel, and everyday life.