atm ↔ kPa
Convert between atmospheres and kilopascals
atm ↔ kPa
Quick Facts
- •1 atm = 101.325 kPa exactly, by definition
- •1 atm = 1.01325 bar = 14.696 psi = 760 mmHg
- •Multiply atm by 101.325 for kPa, divide kPa by 101.325 for atm
- •Every 10 m of sea water adds about 1 atm of pressure
- •Denver at 1,600 m sits near 0.83 atm (84 kPa)
- •Use R = 0.08206 L·atm/(mol·K) when pressure is in atmospheres
Atmospheres and Kilopascals
One standard atmosphere (atm) equals 101.325 kPa. The atmosphere is a reference unit based on the average air pressure at sea level. It's commonly used in chemistry (for gas laws), diving (depth pressure), and physics. Every 10 meters of water depth adds approximately 1 atm of pressure.
How to Convert atm to kPa by Hand
Multiply the number of atmospheres by 101.325 to get kilopascals. Going the other way, divide kilopascals by 101.325. So 2 atm is 202.65 kPa, 0.5 atm is 50.66 kPa, and 250 kPa is 2.467 atm. For rough mental work, treating 1 atm as 100 kPa is accurate to within 1.3 percent, which is close enough for weather talk but not for lab work or gas law problems where the exact figure matters.
Where the Number 101.325 Comes From
The standard atmosphere is a defined constant, not a measurement. It was fixed in 1954 as exactly 101,325 pascals, chosen because it matches the average sea level air pressure at 15 degrees Celsius at a latitude of 45 degrees. The pascal itself is one newton of force spread over one square meter, which is a very small pressure, hence the kilo prefix in everyday use. Because 1 atm is defined rather than measured, the conversion is exact and never needs updating.
Using atm in Gas Law Problems
The ideal gas law, PV = nRT, is where most students meet this conversion. The gas constant R takes different values depending on which pressure unit you use: 0.08206 L·atm/(mol·K) when pressure is in atmospheres, or 8.314 J/(mol·K) when pressure is in pascals and volume is in cubic meters. Mixing the two is the most common source of answers that are off by a factor of about 100. Decide on your unit system before you start, convert every pressure into it, then pick the matching R.
Diving, Altitude and Real Pressure Changes
Sea water adds roughly one atmosphere of pressure for every 10 meters of depth, so a diver at 20 meters experiences about 3 atm total: one from the air above and two from the water. That is 304 kPa. Going the other way, pressure falls with altitude. Denver sits at about 0.83 atm, or 84 kPa, which is why baking recipes and boiling times change there. The summit of Everest is near 0.33 atm, or 33 kPa, roughly a third of the oxygen available at sea level.
How atm Compares to Other Pressure Units
One atmosphere is 101.325 kPa, 1.01325 bar, 14.696 psi, 760 mmHg, and 760 torr. The bar was deliberately defined as 100 kPa so it would sit close to one atmosphere while being a round metric number, which is why European tyre gauges and weather charts favour it. Engineers in the United States generally use psi, medicine uses mmHg for blood pressure, and meteorologists use hectopascals, where 1 hPa equals 100 Pa, making standard pressure a tidy 1013.25 hPa.
Understanding the atm ↔ kpa
One standard atmosphere (atm) equals exactly 101.325 kilopascals. To convert atm to kPa, multiply by 101.325. To convert kPa to atm, divide by 101.325. The atmosphere is based on average air pressure at sea level, while the kilopascal is the SI unit used on tire gauges, weather maps and lab equipment outside the US.
Worked examples
What is 101.325 kPa in atm?
- 1Divide by 101.325: 101.325 ÷ 101.325 = 1.
101.325 kPa is exactly 1 atm, the standard sea-level air pressure.
A tire is inflated to 220 kPa. What is that in atm?
- 1Divide by 101.325: 220 ÷ 101.325 = 2.171.
- 2Tire gauges read gauge pressure, which is above the surrounding air. Add 1 atm for absolute pressure: 3.171 atm.
220 kPa gauge is about 2.17 atm above the air around it, or 3.17 atm absolute. It is also about 32 psi.
A diver is at 3 atm absolute. What is that in kPa?
- 1Multiply by 101.325: 3 × 101.325 = 303.975.
3 atm is about 304 kPa, roughly the pressure 20 meters under seawater.
kPa to atm reference table
Common pressure values with their atm, psi and bar equivalents.
| kPa | atm | psi | bar | Where you see it |
|---|---|---|---|---|
| 50 | 0.493 | 7.25 | 0.50 | Air near the top of Everest (about 34 kPa) |
| 80 | 0.790 | 11.60 | 0.80 | Airliner cabin at cruise |
| 100 | 0.987 | 14.50 | 1.00 | One bar, weather maps |
| 101.325 | 1.000 | 14.70 | 1.013 | Standard sea-level pressure |
| 200 | 1.974 | 29.01 | 2.00 | Car tire (gauge) |
| 220 | 2.171 | 31.91 | 2.20 | Car tire, common spec |
| 250 | 2.467 | 36.26 | 2.50 | SUV tire (gauge) |
| 300 | 2.961 | 43.51 | 3.00 | Bike tire, road |
| 500 | 4.935 | 72.52 | 5.00 | Espresso machine pump side |
| 1000 | 9.869 | 145.04 | 10.00 | Espresso extraction (about 9 bar) |
Values are rounded. 1 atm = 101.325 kPa = 14.696 psi = 1.01325 bar = 760 mmHg.
Practical tips
- •For quick estimates, treat 1 atm as 100 kPa. The error is about 1 percent.
- •In chemistry, check whether a problem uses STP at 1 atm or 1 bar. Textbooks differ.
Frequently asked questions
This calculator is for educational and reference purposes only. Always verify critical calculations independently.