ATM to Pascals Conversion
Enter a pressure in atmospheres (atm) or pascals (Pa) and every output updates instantly. The converter works in both directions and also shows the equivalent in kilopascals, megapascals, bar, PSI, millimetres of mercury and millibar. A step-by-step panel shows the exact arithmetic, and a reference table lists common pressure benchmarks.
Formula
Worked example
3.5 atm x 101,325 Pa/atm = 354,637.5 Pa. Divide by 1,000 for 354.64 kPa. Divide by 1,000,000 for 0.354638 MPa. Multiply by 14.696 for 51.44 PSI, and multiply by 760 for 2,660 mmHg.
The standard atmosphere and the pascal
The standard atmosphere (symbol: atm) is defined as exactly 101,325 pascals. This value was adopted by the International Union of Pure and Applied Chemistry (IUPAC) and the International Bureau of Weights and Measures (BIPM) as the reference pressure at sea level. The pascal (Pa) is the SI derived unit of pressure, equal to one newton per square metre (N/m2). Because everyday pressures are so much larger than one pascal, kilopascals (kPa = 1,000 Pa) and megapascals (MPa = 1,000,000 Pa) are widely used in engineering and science.
How to convert atm to pascals
The conversion is a simple multiplication: P(Pa) = P(atm) x 101,325. For the reverse, divide: P(atm) = P(Pa) / 101,325. Because 101,325 is exact by definition, no rounding is introduced in the first step - only your input itself carries any uncertainty. For intermediate units, one bar equals exactly 100,000 Pa, so 1 atm = 1.01325 bar. One kilopascal equals 1,000 Pa, so 1 atm = 101.325 kPa. One PSI equals 6,894.757 Pa, so 1 atm equals approximately 14.696 PSI.
Unit guide: when to use Pa, kPa, bar or PSI
The pascal is the officially correct SI unit but is inconveniently small for most practical pressures: atmospheric pressure is 101,325 of them. Kilopascals are common in tyre pressure specifications in metric countries, weather reports (hectopascals = 100 Pa each), and blood pressure reference values. Bar is widely used in European industry and for gas-cylinder ratings. PSI dominates US automotive, industrial, and plumbing contexts. Millimetres of mercury (mmHg) remain standard in medicine and blood pressure measurement. Millibar is the meteorological standard in many countries. This converter shows all of them together so you can switch between contexts without separate tools.
Pressure measurement in science and engineering
In physics and chemistry, atmospheric pressure sets a baseline for many experiments. Gas-law calculations (Boyle's law, the ideal-gas law) require absolute pressure in pascals or atmospheres. In engineering, gauge pressure (pressure above ambient) is common for pipes and vessels, so a gauge reading of 1 atm corresponds to an absolute pressure of 2 atm (202,650 Pa). In meteorology, standard sea-level pressure is 1013.25 hPa (hectopascals), which is the same as 1 atm or 1013.25 mbar. Deep-sea research uses megapascals: 1 km of seawater adds roughly 9.81 MPa (about 97 atm) of pressure.
Common pressure benchmarks
| Pressure context | atm | Pa | kPa | PSI |
|---|---|---|---|---|
| Near-perfect vacuum | 0 | 0 | 0 | 0 |
| Mars surface (avg) | 0.006 | 600 | 0.60 | 0.087 |
| Standard sea-level atmosphere | 1.000 | 101,325 | 101.3 | 14.70 |
| Car tyre (typical) | 2.5 | 253,313 | 253.3 | 36.75 |
| Bicycle tyre (road) | 7.0 | 709,275 | 709.3 | 102.9 |
| Scuba tank (full) | 200 | 20,265,000 | 20,265 | 2,939 |
| Deep ocean (10 km) | 1,086 | 110,000,000 | 110,000 | 15,954 |
| Autoclave (sterilisation) | 2.0 | 202,650 | 202.7 | 29.39 |
Approximate values for everyday and scientific reference points.
Frequently asked questions
What is 1 atm in pascals exactly?
1 atm is defined as exactly 101,325 Pa. This is not an approximation - it is the official SI definition of the standard atmosphere adopted by the BIPM and IUPAC. So 2 atm = 202,650 Pa, 0.5 atm = 50,662.5 Pa, and so on.
How do I convert pascals back to atm?
Divide the number of pascals by 101,325. For example, 303,975 Pa / 101,325 = 3 atm exactly. Use the "Pascals to Atmospheres" direction in this converter to do it instantly without any arithmetic.
What is the difference between atm and bar?
1 bar is exactly 100,000 Pa, while 1 atm is 101,325 Pa. The two units differ by about 1.3 percent. Bar is a metric unit widely used in industrial and European contexts, while atm is the physically defined standard atmosphere tied to sea-level pressure on Earth.
Why are there so many pressure units?
Pressure units evolved independently in different fields before SI standardisation. Medicine adopted mmHg (torr) from early mercury manometers. Engineering in the US used PSI because the imperial system was already in place. Meteorology settled on millibar (and later hectopascal). Science uses Pa. Trade and industry in Europe shifted to bar. This converter shows all of them together.
How does atmospheric pressure change with altitude?
Pressure falls roughly exponentially with altitude. At sea level, pressure is 1 atm (101,325 Pa). At 5,500 m above sea level it is approximately 0.5 atm (50,663 Pa). At cruising altitude for commercial aircraft (about 10,600 m), cabin pressure is typically held at around 0.75 atm (75,994 Pa) even though outside pressure is only about 0.26 atm.
Is 1 atm the same as 1 bar?
No, they are close but not equal. 1 atm = 101,325 Pa, while 1 bar = 100,000 Pa exactly. The difference is 1,325 Pa or about 1.3 percent. For everyday engineering estimates the two are often used interchangeably, but for precise scientific work you must use the correct conversion factor.