ATM to kPa conversion: formula and quick reference table

ATM and kPa are two units expressing pressure on the same scale. One atmosphere is exactly 101.325 kPa, a defined constant in the SI system. This guide covers the direct conversion, the formula, and a reference table for pressures you'll encounter in everyday contexts—from tire gauges to laboratory work to diving. It is educational only.

The conversion: 1 atm = 101.325 kPa

Atmosphere (atm) and kilopascal (kPa) measure the same thing: force per unit area. The pascal (Pa) is the SI unit; one atm is defined as exactly 101,325 Pa by international agreement at the Bureau International des Poids et Mesures (BIPM). Since 1 kPa = 1,000 Pa, it follows that 1 atm = 101.325 kPa, precisely.

This definition is fixed, not derived from measuring the actual air pressure at sea level on a particular day. Real atmospheric pressure at sea level varies between roughly 95 and 105 kPa depending on weather and elevation. The standard atmosphere is a reference constant, like standard temperature (273.15 K or 0°C), used so that pressures can be stated and compared unambiguously across the world and across time.

How to convert between atm and kPa

ATM to kPa: multiply by 101.325

kPa = atm × 101.325

kPa to atm: divide by 101.325

atm = kPa ÷ 101.325

The factor 101.325 is exact; it comes directly from the definition. For a worked example: a diving tank at 200 bar gauge pressure is 200 kPa (bar and kPa are nearly equal—1 bar = 100 kPa), which converts to about 1.97 atm. A laboratory at 0.95 atm (low pressure used for vacuum work) is about 96.26 kPa.

Reference table: common atm to kPa values

Here are the pressures you will encounter most often, in both units:

The atm unit is most common in chemistry and diving, where pressures are often quoted relative to standard atmosphere. The kPa unit is standard in engineering and SI applications. Many modern pressure gauges show both, or switch between them. Our ATM to kPa converter performs the calculation instantly; use this table for a quick mental check or when a reference is needed.

The difference: atm, bar, psi, and other pressure units

Pressure can be expressed in many units, each with a historical or practical origin. A quick map of the most common:

• atm (atmosphere): exactly 101.325 kPa. Used in science and diving as a reference.
• kPa (kilopascal): 1,000 Pa, the SI unit. Used in engineering, weather, and modern scientific work.
• bar: exactly 100 kPa. Very close to 1 atm (off by 1.325%), widely used in Europe and diving computers. Not an SI unit, but legally acceptable in Europe.
• psi (pounds per square inch): ~6.894 kPa. The customary US unit; common on tire gauges and pressure gauges in North America.
• mmHg (millimeters of mercury): 0.1333 kPa per mmHg. Used in medicine (blood pressure) and laboratories; 760 mmHg = 1 atm exactly.

Because atm and bar are so close (1.325% difference), the distinction is easy to overlook—but in systems that must match exactly, like dive computers or laboratory records, the confusion between them has caused errors. Divers, in particular, encounter this constantly; our guide to scuba tank pressures explores how the atm/bar distinction matters in dive planning. Always verify which unit a reading is in before relying on it.

Why 101.325 and not a round number?

The number 101.325 seems arbitrary, but it has a historical reason. One atmosphere was originally defined as the average air pressure at sea level on a normal day, measured with a mercury barometer. That pressure supported a 760 mm tall column of mercury. When the pascal (the SI pressure unit) was adopted in the 1960s, the atm was redefined as exactly 101,325 Pa to preserve the historical value while connecting it to SI. The "325" in 101.325 kPa comes from that 760 mmHg definition: 760 mmHg = 101.325 kPa. Modern definitions are constants, not averages, so they are reproducible and don't drift with weather or location.