Atmosphere Converter
Unit ConversionConvert standard atmospheres to pascals, hPa, kPa, MPa, bar, torr, mmHg, inHg, psi and technical atmospheres. Type into any box and every other unit updates.
Atmosphere
Metric
Mercury and Vacuum
Other Units
1 Atmosphere = 101,325 Pascals ⟷ 1 Pascal = 0.00000986923 Atmospheres
1 Atmosphere = 1,013.25 Hectopascals / Millibars ⟷ 1 Hectopascal / Millibar = 0.000986923 Atmospheres
1 Atmosphere = 101.325 Kilopascals ⟷ 1 Kilopascal = 0.00986923 Atmospheres
1 Atmosphere = 0.101325 Megapascals ⟷ 1 Megapascal = 9.869233 Atmospheres
1 Atmosphere = 1.01325 Bar ⟷ 1 Bar = 0.986923 Atmospheres
1 Atmosphere = 760 Torr ⟷ 1 Torr = 0.00131579 Atmospheres
1 Atmosphere = 759.999892 mmHg ⟷ 1 mmHg = 0.00131579 Atmospheres
1 Atmosphere = 29.921256 Inches of Mercury (inHg) ⟷ 1 Inch of Mercury (inHg) = 0.0334211 Atmospheres
1 Atmosphere = 14.695949 PSI ⟷ 1 PSI = 0.068046 Atmospheres
1 Atmosphere = 1.033227 Technical Atmospheres (at) ⟷ 1 Technical Atmosphere (at) = 0.967841 Atmospheres
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Unit Conversion calculators
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SponsoredThis atmosphere converter shows a pressure in standard atmospheres (atm) next to pascals, hectopascals, kilopascals, megapascals, bar, torr, millimeters and inches of mercury, psi and technical atmospheres. Type into any box and the others update as you type.
The standard atmosphere is a fixed reference value, exactly 101,325 pascals, set in 1954 and close to average air pressure at sea level. It is not the air pressure at any particular place or time. Chemistry, physics and gas calculations use it as a convenient unit for pressures near and above everyday air pressure.
Atmospheres here measure absolute pressure, which cannot be negative, so a negative entry clears the other boxes. Results show up to six decimal places.
Standard Atmospheric Pressure
In 1954 the General Conference on Weights and Measures adopted the standard atmosphere as exactly 101,325 newtons per square meter, which is 101,325 pascals. NOAA uses the same standard for sea level, quoted in weather units as 29.92 inches of mercury or 1,013.25 millibars. The table shows atmospheric pressure in psi, kPa, mmHg, hPa and other units.
| Unit | 1 Standard Atmosphere | Value Status |
|---|---|---|
| Pascals | 101,325 Pa | Exact |
| Kilopascals | 101.325 kPa | Exact |
| Hectopascals / Millibars | 1,013.25 hPa | Exact |
| Bar | 1.01325 bar | Exact |
| PSI | 14.695949 psi | Rounded |
| mmHg | 759.999892 mmHg | Rounded |
| Torr | 760 Torr | Exact |
| Inches of Mercury (inHg) | 29.921256 inHg | Rounded |
Real air pressure falls as you climb, so at altitude it is below one atmosphere. The Oxygen Saturation Altitude Estimator looks at what that thinner air means for blood oxygen.
Standard Temperature and Pressure
Standard temperature and pressure (STP) sets a reference state for comparing gases. The IUPAC Green Book notes that a standard pressure of 1 bar (100 kPa) has been recommended since 1982; before that, 101,325 Pa (one atmosphere) was usually used. Both are still found in textbooks, so check which one a problem means.
The choice changes the molar volume of an ideal gas at 0 °C: 22.710981 liters per mole at 100 kPa, and 22.413996 liters per mole at 101.325 kPa (IUPAC values).
The Ideal Gas Law Calculator takes pressure in atmospheres and temperature in kelvins; the Temperature Converter turns 0 °C into 273.15 K.
Chemistry classes usually want answers to the right number of significant figures: 745.0 mmHg has four, so its value in atmospheres should too. The Significant Figures Calculator rounds a result that way.
Atmosphere, Bar and Torr
Bar vs ATM
The bar and the standard atmosphere are close but not equal. 1 bar is exactly 100,000 Pa and 1 atm is exactly 101,325 Pa, so 1 atm = 1.01325 bar and 1 bar is about 0.986923 atm, about 1.3% less.
Torr vs mmHg
The torr is defined as exactly 1/760 of a standard atmosphere, so 1 atm = 760 Torr. The conventional millimeter of mercury is defined from mercury density and standard gravity as exactly 133.322387415 Pa, slightly more than a torr (about 133.322368 Pa). The difference is under one part in a million, so 1 atm is about 759.99989 mmHg, and most work treats the two as equal.
The Technical Atmosphere
The technical atmosphere (at) is a different, older unit: one kilogram-force per square centimeter, exactly 98,066.5 Pa. 1 at is about 0.967841 atm. It still appears on older gauges as kgf/cm².
Atmosphere Conversions
Single conversions that start from or end in this page's units, one page per pair.
- Bar to Atmospheres Converter: 1 bar is about 0.986923 standard atmospheres
- Kilopascals to Atmospheres Converter: 1 kilopascal is about 0.00986923 standard atmospheres
- Atmospheres to Pascals Converter: 1 standard atmosphere equals exactly 101,325 pascals
- PSI to Atmospheres Converter: 1 psi is about 0.068046 standard atmospheres
- mmHg to Atmospheres Converter: 1 millimeter of mercury is about 0.00131579 standard atmospheres
- Torr to Atmospheres Converter: 1 torr is about 0.00131579 standard atmospheres
- kgf/cm² to PSI Converter: 1 kilogram-force per square centimeter is about 14.223343 psi
Other Pressure Converters
Each converter below shows one pressure in many units at once, starting from a different unit.
- Pressure Unit Converter: one pressure in every common unit at once
- PSI Converter: psi to bar, kPa, atm, inHg, inches of water and more
- Kilopascal Converter: kilopascals to psi, bar, atm, hPa and more
- Megapascal Converter: megapascals to psi, ksi, bar, GPa and more
- Pascal Converter: pascals to hPa, kPa, MPa, GPa, psi and more
- Barometric Pressure Converter: inches of mercury to hPa, millibars, mmHg and more
Frequently Asked Questions
What does atm stand for?
atm is the symbol for the standard atmosphere, a unit of pressure equal to exactly 101,325 pascals. It has nothing to do with cash machines, which share the abbreviation.
What is 1 atm in kPa?
1 atm is exactly 101.325 kPa.
Which measurement describes the pressure of a gas?
Gas pressure is force per unit area, so it is measured in pressure units: pascals or kilopascals in SI, standard atmospheres, millimeters of mercury or torr in chemistry, and psi in US engineering. Chemistry courses most often work in atm, mmHg and kPa, and all three convert in the boxes above.
How many psi is 1 atm?
1 atm is about 14.6959 psi, often rounded to 14.7 psi.
Does the standard atmosphere change with altitude?
No. The standard atmosphere is a fixed unit, so 1 atm is always 101,325 pascals and the conversion factors never change. What changes with altitude and weather is the real air pressure, which you can measure in atmospheres or any other unit.
Why can't I enter a negative atmosphere value?
Atmospheres here measure absolute pressure, counted from a perfect vacuum, and nothing is below a perfect vacuum. Gauge readings below the surrounding air can be negative; the PSI and kPa converters accept those.
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