atm – Standard Atmosphere Pressure Unit

Standard Atmosphere is mainly used as a reference value for the average atmospheric pressure at sea level. It is often used to indicate the depth rating for a water resistant watch, but otherwise is rarely used as a unit for measuring pressure. 1 standard atmosphere is defined as being exactly equal to 101,325 pascals.

Since the atmospheric pressure varies with changes in weather and altitude, it is convenient to standardise on a single value so that ratings, measurements and specifications can be compared. In particular 1 Standard Atmosphere is used by the Aviation industry as the reference standard for sea level pressure.

In the table below you will find the equivalent values for 1 atm in other pressure units.

To calculate the number of atmospheres for a pressure value in other units please click on the relevant unit link below.

For converting many readings to or from atmospheres please use our pressure unit calculator.

Conversion Factors

• 1.01325 bar
• 14.6959 psi
• 1013.25 mbar
• 101325 N/m²
• 101325 Pa
• 1013.25 hPa
• 101.325 kPa
• 0.101325 MPa
• 1.03323 kg/cm²
• 10332.3 mmH2O 4°C (39.2°F)
• 1033.23 cmH2O 4°C (39.2°F)
• 10.3323 mH2O 4°C (39.2°F)
• 406.782 inH2O 4°C (39.2°F)
• 33.8985 ftH2O 4°C (39.2°F)
• 760 mmHg 0°C (32°F)
• 76 cmHg 0°C (32°F)
• 29.9213 inHg 0°C (32°F)
• 760 Torr
• 760000 mTorr
• 1 atm
• 1.03323 at
• 1013250 dyn/cm²
• 235.135 oz/in²
• 760000 µHg 0°C (32°F)
• 0.00656069 tsi (uk, long)
• 0.00734797 tsi (usa, short)
• 1.05811 tsf (usa, short)
• 2116.22 psf
• 1033.23 g/cm²

Please note that the conversion factors above are accurate to 6 significant figures.

Help

Atmospheric pressure in inHg units

What does one atmospheric pressure equal in inches of mercury?

The standard constant value used for atmospheric pressure at sea level is 1 atm (standard atmosphere) which equals 101325 pascals in SI units, and is equivalent to 29.9213 inches of mercury.

1 atm to mmHg

1 atmosphere is equal to how many mmHg?

1 atmosphere (atm) = 760.000 mmHg (millimetres of Mercury)

Average atmospheric pressure at sea level

What is the average pressure on Earth at sea level in bar pressure?

The internationally accepted ‘standard’ value at sea level is 1.01325 bar. Since the actual pressure at sea level varies in an unpredictable way due to constant changes in weather conditions, an overall true average is not practical to determine or use universally because it would need to be constantly iterated to keep up with climatic variations. So 1.01325 bar is not a real average as such, but used more as a sensible value that has been chosen as the representative average pressure for the Earth’s atmosphere at sea level.

The standard atmosphere value has many uses in atmospheric calculations and one example of this is the FAA procedures for setting aircraft altimeters at altitudes of 18,000 feet and above to ensure all aircraft are using the same pressure reference when measuring the height above sea level.