Millimeters of mercury to atmospheres (mmHg to atm) converter
What are millimeters of mercury and atmospheres?
Millimeters of mercury (mmHg)
The millimeter of mercury (mmHg) is a unit of pressure originally defined by the height of a mercury column that a given pressure can support. One millimeter of mercury is the pressure exerted by a one-millimeter-tall column of mercury under standard gravity. It remains the everyday unit for blood pressure readings in medicine and for vacuum and atmospheric measurements in many laboratories, where instruments such as mercury barometers and sphygmomanometers report directly in mmHg.
Standard atmospheres (atm)
The standard atmosphere (atm) is a unit of pressure defined as the average air pressure at sea level. It is a convenient reference point because so many physical and chemical processes are described relative to “atmospheric” conditions. Chemists quote gas pressures in atmospheres, and the unit appears throughout thermodynamics, diving, and weather science whenever a pressure is compared against the familiar baseline of the air around us.
How does the calculator work?
This converter links the two pressure units in both directions. Type a value into either field and the other updates instantly. The tool remembers which field you changed last, so it always converts from the value you entered to the matching result.
The conversion rests on a single definition: one standard atmosphere equals exactly 760 millimeters of mercury. Going the other way, you divide by that same number.
Millimeters of mercury and atmospheres conversion formulas
To convert millimeters of mercury to atmospheres, divide by 760:
To convert atmospheres back to millimeters of mercury, multiply by the same factor:
Conversion table
The table below shows how the two pressure units relate to each other.
| Pressure unit | Millimeters of mercury (mmHg) | Standard atmospheres (atm) |
|---|---|---|
| 1 Millimeter of mercury | 1 | 0.0013158 |
| 1 atm | 760 | 1 |
For related conversions, see the pressure unit converter.
Examples
The following examples reuse the same numbers as the calculator’s test fixtures.
Example 1: Convert 760 mmHg to atm
Starting from seven hundred sixty millimeters of mercury:
So 760 mmHg is exactly 1 atm.
Example 2: Convert 120 mmHg to atm
For a typical systolic blood-pressure reading:
Thus 120 mmHg equals about 0.1579 atm.
Example 3: Convert 2 atm to mmHg
Working in the other direction with two atmospheres:
So 2 atm is 1520 mmHg.
Practical applications
Pressure conversion is routine whenever clinical, scientific, and engineering units meet. Medical staff read blood pressure in mmHg, while a physiology textbook might express the same value relative to atmospheric pressure, so converting connects the bedside reading to the underlying physics.
In chemistry and physics, gas-law problems are often set up in atmospheres, yet barometers and vacuum gauges frequently report in millimeters of mercury, so converting keeps the numbers consistent within a single calculation.
Divers and weather enthusiasts also use this conversion when an instrument reads in one unit but the reference data, such as a standard-conditions table, is quoted in the other.
Frequently asked questions
How do I convert mmHg to atm?
Divide the mmHg value by 760. For example, 760 mmHg ÷ 760 = 1 atm.
How many millimeters of mercury are in one atmosphere?
One standard atmosphere equals exactly 760 millimeters of mercury.
How many atmospheres are in one mmHg?
One millimeter of mercury equals about 0.0013158 atm.
How do I convert atm to mmHg?
Multiply the atm value by 760. For example, 2 atm × 760 = 1520 mmHg.
What is a normal blood pressure in atm?
A typical reading of 120 mmHg is about 0.158 atm, since 120 ÷ 760 ≈ 0.1579 atm.