What this calculator does
This tool converts a pressure value from standard atmospheres (atm) into pascals (Pa), the SI unit of pressure. Enter a value in atm and the calculator multiplies it by 101,325 to return the equivalent pressure in pascals, along with the same result in kilopascals (kPa) for convenience.
The formula
The conversion is a fixed, exact multiplication because the standard atmosphere is a defined unit, not a measured one:
Pascals = Atmospheres × 101,325
By international agreement (adopted by the International Bureau of Weights and Measures), 1 standard atmosphere is defined as exactly 101,325 Pa. There is no rounding or approximation in the definition itself, so this conversion is exact to as many decimal places as you need. To go the other direction, divide a pascal value by 101,325 to get atmospheres. Because 1 kPa = 1,000 Pa, dividing the pascal result by 1,000 gives kilopascals, which is the unit most weather reports, tire gauges, and engineering datasheets actually use.
Why pascals and atmospheres are both still used
The pascal (defined as one newton per square meter) is the official SI unit of pressure and is what you'll see in physics, engineering, and most modern scientific work. The atmosphere, by contrast, is a legacy unit rooted in the historical average air pressure at sea level. It survives because it's an intuitive reference point: "1 atm" instantly communicates "roughly sea-level air pressure," whereas "101,325 Pa" does not carry the same immediate meaning to most people. You'll still see atm used in chemistry (standard temperature and pressure, gas law problems), diving and hyperbaric medicine, and some industrial pressure ratings, while pascals (and their multiples, kPa and MPa) dominate structural engineering, meteorology (in hectopascals), and SI-based scientific literature.
Reference points worth knowing
- 1 atm = 101,325 Pa = 101.325 kPa — standard atmospheric pressure at sea level.
- 0.5 atm ≈ 50,662.5 Pa — roughly the air pressure at 5,500 meters (18,000 ft) altitude.
- 2 atm = 202,650 Pa — the ambient pressure at about 10 meters underwater, a common reference in scuba diving.
- 1 bar = 100,000 Pa, which is very close to but not identical to 1 atm — a frequent source of confusion since the two are often used interchangeably in casual contexts even though they differ by about 1.3%.
- 1 atm ≈ 14.696 psi, useful if you're cross-checking against pounds per square inch, the common unit on US tire gauges and pressure vessels.
Worked examples
Example 1: Convert 1 atm to pascals. 1 × 101,325 = 101,325 Pa (101.325 kPa).
Example 2: Convert 3 atm (a typical pressure cooker operating pressure above atmospheric, though ratings vary) to pascals. 3 × 101,325 = 303,975 Pa (303.975 kPa).
Example 3: Convert 0.9 atm, roughly the pressure at 1,000 meters elevation, to pascals. 0.9 × 101,325 = 91,192.5 Pa (91.1925 kPa).
Frequently asked questions
Is 1 atm exactly 101,325 Pa, or is that rounded? It is exact. The standard atmosphere was fixed by international standards bodies as precisely 101,325 Pa, so there is no measurement uncertainty in the conversion factor itself.
Is atm the same as bar? No, though they're close. 1 bar = 100,000 Pa exactly, while 1 atm = 101,325 Pa — a difference of about 1,325 Pa, or roughly 1.3%.
How do I convert pascals back to atmospheres? Divide the pascal value by 101,325. For example, 200,000 Pa ÷ 101,325 ≈ 1.9738 atm.
Why do weather forecasts use hectopascals instead of pascals? A hectopascal (hPa) equals 100 Pa, which keeps typical sea-level readings (around 1,013.25 hPa) in a convenient range similar to the older unit "millibar" (1 hPa = 1 mbar), so meteorologists adopted it for continuity.
What's the difference between atmospheric pressure and gauge pressure? Atmospheric pressure is measured relative to a vacuum (absolute pressure). Gauge pressure, common on tire gauges and pressure cookers, is measured relative to the surrounding atmosphere, so a gauge reading of 0 corresponds to roughly 101,325 Pa absolute.