How this calculator works
The standard atmosphere is a defined reference pressure of exactly 101,325 Pa, close to the average sea-level pressure. One kilopascal is 1,000 Pa, so 101.325 kPa is exactly one atmosphere. Weather services often report pressure in hectopascals or kilopascals, while chemistry and engineering texts use atmospheres. Converting is a single division by 101.325 once the value is in kilopascals.
Formula
atm = kPa / 101.325. kPa = atm x 101.325. The standard atmosphere is exactly 101,325 Pa by definition.
Worked example
101.325 kPa = 1 atm. 100 kPa = 0.986923 atm. 1 kPa = 0.00986923 atm. 202.65 kPa = 2 atm. 50 kPa = 0.493462 atm.
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Frequently asked questions
Why is one atmosphere 101.325 kPa and not 100 kPa?
The atmosphere was defined as a round number in older units, 760 mmHg, before the pascal existed. That historical definition became exactly 101,325 Pa. A round 100 kPa is one bar, which is close but not identical.
How do hectopascals relate to kilopascals?
Hectopascals are 100 Pa and kilopascals are 1,000 Pa, so 1 kPa equals 10 hPa. A weather map value of 1,013 hPa is 101.3 kPa, or about one atmosphere.
Is this gauge or absolute pressure?
The conversion is arithmetic only and does not change the reference point. A gauge pressure of 100 kPa is 100 kPa above the local atmosphere, not an absolute pressure of one atmosphere plus 100 kPa.
Why does a pressure reading change with altitude?
Atmospheric pressure falls with height because there is less air above. Sea-level pressure is near 101.3 kPa, while a high mountain can see readings below 70 kPa.