Atmospheres to Pascals Converter
1 atm = 101,325 Pa exactly. Type in either box.
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Exactly 101,325 pascals
The standard atmosphere is defined as exactly 101,325 pascals. Not approximately, not as measured on a particular day — that number is the definition of the unit.
1 atm = 101,325 Pa exactly
The value was chosen in 1954 to sit near average sea-level air pressure, and it does, but the two are now separate things. What the barometer reads today is weather; the standard atmosphere is a constant.
Pascal figures at this scale are unwieldy, so the same pressure is usually written 101.325 kPa or 1013.25 hPa. Weather maps use the last of those.
The standard atmosphere
One atmosphere is defined as exactly 101,325 pascals. It was originally meant to represent average air pressure at sea level, and it is close, but it is now a fixed definition rather than a measurement — real sea-level pressure wanders either side of it with the weather.
The unit is used where pressure is being compared to ordinary air: chemistry, diving, aviation and physiology. Ten metres of seawater adds roughly one atmosphere, which is the rule every diver learns first.
The pascal
The pascal is the SI unit of pressure: one newton spread over one square metre. That is a very small amount of force over a fairly large area, so the pascal itself is a tiny unit — a sheet of paper resting on a table exerts roughly one pascal. Atmospheric pressure is about 101,325 of them.
Because the unit is so small, it is almost always used with a prefix. Kilopascals for weather and tyres, megapascals for material strength, hectopascals for the numbers on a weather map.
The working, step by step
Every line updates with whatever you type above. The point is the method, which is the same for any pair of units in this family.
The same quantity, two different numbers
One physical amount, read off two scales. The tick marks do not line up, and the gap between them is the conversion factor made visible.
How much is that?
A number is easier to judge next to something familiar.
Your turn
Reading a method and being able to use it are different things. Answer within half a per cent and it counts as correct.
Score: 0 of 0
How to use this converter
- Type into either box. The other side updates as you go; there is no button to press.
- Swap the direction with the button between the boxes, carrying your value across.
- Set the decimals if the default is more or less precision than you need.
- Copy the answer with its unit, ready to paste.
- Use the shortcut buttons for the values that come up most often.
- Share the result. The address bar tracks what you type, so the link you copy opens on the same number.
Common uses and tips
Where pressure conversions come up
- Tyres. The single most common reason anyone converts pressure. American placards are in psi, European and Asian ones in bar or kPa, and the three appear side by side on the same door sticker.
- Weather. Forecasts use hectopascals or millibars, which are the same size — 1 hPa is 1 mbar. A typical high-pressure system reads about 1020 of either.
- Diving. Cylinder pressures are in bar almost everywhere and psi in the United States. A full 200 bar cylinder is about 2,900 psi.
- Coffee. Espresso machines are specified in bar; nine bar at the group head is the usual target, which is about 130 psi.
- Materials and hydraulics. Tensile strength and hydraulic ratings come in MPa or psi, and the two communities rarely use the same one.
The trap: gauge pressure and absolute pressure
Almost every pressure you read off a dial in daily life is gauge pressure — how much higher than the surrounding air it is. A tyre at 32 psi contains 32 psi more than the atmosphere, so its absolute pressure is about 46.7 psi.
Conversion between units never changes which of the two you have. If you start with a gauge reading you end with a gauge reading. Where it goes wrong is in physics and chemistry, where the gas laws need absolute pressure: add one atmosphere to a gauge figure before it goes into a calculation. The units psig and psia exist precisely to keep the two apart.
Tips worth knowing
- One bar is not one atmosphere. It is 0.9869 of one. The difference is small enough to ignore for a tyre and large enough to matter in a laboratory.
- Millibars and hectopascals are identical. Weather maps use whichever the local service prefers; the number is the same.
- One MPa is about ten atmospheres, which makes megapascals easy to sanity-check against everyday pressures.
- Torr and mmHg are interchangeable in practice, differing by about one part in seven million.
Values people look up most
Each one opens the converter with the number already in it.
- 0.5 atm to Pa
- 1 atm to Pa
- 1.5 atm to Pa
- 2 atm to Pa
- 3 atm to Pa
- 4 atm to Pa
- 5 atm to Pa
- 10 atm to Pa
- 20 atm to Pa
- 50 atm to Pa
- 100 atm to Pa
- 200 atm to Pa
- 500 atm to Pa
Quick reference
| Atmospheres | Pascals |
|---|---|
| 0.5 atm | 50,662.5 Pa |
| 1 atm | 101,325 Pa |
| 2 atm | 202,650 Pa |
| 3 atm | 303,975 Pa |
| 5 atm | 506,625 Pa |
| 10 atm | 1,013,250 Pa |
| 20 atm | 2,026,500 Pa |
| 50 atm | 5,066,250 Pa |
| 100 atm | 10,132,500 Pa |
| 200 atm | 20,265,000 Pa |
| 500 atm | 50,662,500 Pa |
| 1,000 atm | 101,325,000 Pa |
Questions people ask
How many pascals in one atmosphere?
Exactly 101,325 Pa.
Why is it not a round number?
Because the value was chosen to match average sea-level pressure, which is not a round number of pascals.
What is one atmosphere in hPa?
1013.25 hPa, the figure weather maps use.
Does this convert gauge or absolute pressure?
Whichever you put in. Converting units does not change which kind of pressure you have — a gauge reading converts to a gauge reading. If a calculation needs absolute pressure, add one atmosphere first.