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.

**Atmospheric pressure measurement products**

- Outside HVAC 900-1100 mbar abs baro range 4-20mA signal pressure sensor
- LEX1 (Ei) High Accuracy Digital Pressure Gauge
- 550-1100mbar absolute 4-20mA high resolution air pressure sensor for environmental test chamber use
- 23 to 33 inHg barometric range pressure transducer with a 10 volt hi-resolution output

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Contents

## 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.*

**Atmospheric pressure measurement products**

- Barometric range 800-1100mb IECEx approved intrinsically safe pressure transmitter
- Wind power barometric pressure visual monitor with alarm relay switches
- 700 to 1100 millibar scaled 4 to 20mA output pressure sensor for barometric pressure measurement
- 30 psi barometric pressure transducer with 0-10Vdc out

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## 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.

**Atmospheric pressure measurement products**

- 23 to 33 inHg barometric range pressure transducer with a 10 volt hi-resolution output
- Barometric Pressure Transmitters
- 500-1100 mbar absolute range 0-5 volts output barometric pressure sensor
- 500 to 1200 millibar atmospheric pressure logger with RS232 interface

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## Measurement Unit Related Terms

More pages related to measurement unit technical terms.

- at – Technical Atmosphere Pressure Unit
- bar Pressure Unit
- cmH2O – Centimetres of Water Column at 4 deg C Pressure Unit
- cmHg – Centimetres of Mercury at 0 deg C Pressure Unit
- daPa – Dekapascal Pressure Unit
- dyn/cm² – Dyne per Square Centimetre Pressure Unit
- ftH2O – Feet of Water Column at 4 deg C Pressure Unit
- g – Acceleration due to Gravity
- g/cm² – Grams per Square Centimetre Pressure Unit
- hPa – Hectopascal Pressure Unit
- inH2O – Inches of Water Column at 4 deg C Pressure Unit
- inHg – Inches of Mercury at 0 degrees C Pressure Unit
- kg/cm² – Kilogram per Square Centimetre Pressure Unit
- kg/mm² – Kilogram per Square Millimetre Pressure Unit
- kPa – Kilopascal Pressure Unit
- ksi – Kilopounds per Square Inch Pressure Unit
- mbar – Millibar Pressure Unit
- mH2O – Metres of Water Gauge at 4 deg C Pressure Unit
- mmH2O – Millimetres of Water Column at 4 deg C Pressure Unit
- mmHg – Millimetres of Mercury at 0 deg C Pressure Unit
- MPa – Megapascal Pressure Unit
- mPa – Millipascal Pressure Unit
- mTorr – Millitorr Pressure Unit
- N/cm² – Newton per Square Centimetre Pressure Unit
- N/m2 – Newton per Square Metre Pressure Unit
- N/mm² – Newton per Square Millimetre Pressure Unit
- oz/in² – Ounce per Square Inch Pressure Unit
- Pa – Pascal Pressure Unit
- Pressure
- Pressure Units
- psf – Pounds per Square Foot Pressure Unit
- psi – Pounds per Square Inch Pressure Unit
- Specific Gravity
- Torr Pressure Unit
- tsf – Tons per Square Foot (USA, Short) Pressure Unit
- tsi – Tons per Square Inch (UK, Long) Pressure Unit
- tsi – Tons per Square Inch (USA, Short) Pressure Unit
- Water Density
- µHg – Micron of Mercury at 0 deg C Pressure Unit