Atmospheres to kPa Converter
1 atm = 101.325 kPa exactly. Type in either box.
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101.325, by definition
The standard atmosphere is defined as exactly 101,325 pascals, so this conversion has no rounding in it at all. One atmosphere is 101.325 kilopascals and always will be.
1 atm = 101.325 kPa exactly
It is worth being clear about what the unit means. The standard atmosphere is a fixed quantity, not a measurement of today's weather. Real sea-level pressure moves either side of it — a deep low might read 980 hPa and a strong high 1040 hPa, which is 0.967 and 1.026 atmospheres.
Diving gives the most useful intuition: every 10 m of seawater adds about one atmosphere, so a diver at 30 m is under roughly four atmospheres absolute, or about 405 kPa.
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 kilopascal
A thousand pascals, and the size that suits everyday pressures. Car tyres run at roughly 200–250 kPa, the atmosphere sits at about 101 kPa, and a domestic water supply is usually somewhere between 200 and 500 kPa.
It is the working unit for pressure through most of the metric world, which is why tyre placards in Europe, Australia and Asia are marked in kPa alongside the bar figure.
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 kPa
- 1 atm to kPa
- 1.5 atm to kPa
- 2 atm to kPa
- 2.5 atm to kPa
- 3 atm to kPa
- 4 atm to kPa
- 5 atm to kPa
- 6 atm to kPa
- 8 atm to kPa
- 10 atm to kPa
- 15 atm to kPa
- 20 atm to kPa
- 50 atm to kPa
- 100 atm to kPa
- 200 atm to kPa
Quick reference
| Atmospheres | Kilopascals |
|---|---|
| 0.5 atm | 50.6625 kPa |
| 1 atm | 101.325 kPa |
| 2 atm | 202.65 kPa |
| 3 atm | 303.975 kPa |
| 4 atm | 405.3 kPa |
| 5 atm | 506.625 kPa |
| 10 atm | 1,013.25 kPa |
| 20 atm | 2,026.5 kPa |
| 50 atm | 5,066.25 kPa |
| 100 atm | 10,132.5 kPa |
| 200 atm | 20,265 kPa |
| 500 atm | 50,662.5 kPa |
Questions people ask
How many kPa in one atmosphere?
Exactly 101.325 kPa, by definition.
Is one atmosphere the same as one bar?
No. One bar is 100 kPa, so an atmosphere is 1.325 kPa higher — about 1.3 % more.
Does atmospheric pressure change?
Real air pressure does, with weather and altitude. The standard atmosphere is a fixed reference value and does not.
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.