Pressure Units: PSI, Bar, and kPa for Tires, Pumps, and Weather
October 21, 2026
Pressure is force per unit area, and the units differ by country and application. Tires in the United States are inflated in pounds per square inch (PSI), while European tire gauges often read in bar. Weather forecasts use hectopascals or millibars, aviation uses inches of mercury, and engineering uses kilopascals or megapascals. All of them measure the same physical quantity.
The key equivalences: 1 bar = 100 kPa = 14.5038 PSI, and standard atmospheric pressure is 101.325 kPa = 1.01325 bar = 14.696 PSI. So a tire pressure of 32 PSI is 32 ÷ 14.5038 = 2.21 bar, or 220.6 kPa.
Skip the math and get your answer instantly:
Open the Weight Converter →Conversion Table
To convert, multiply by the factor shown. Remember that most of these are exact or very precise definitions.
| From | To | Multiply by |
|---|---|---|
| PSI | kPa | 6.89476 |
| PSI | bar | 0.0689476 |
| bar | PSI | 14.5038 |
| bar | kPa | 100 |
| atm | kPa | 101.325 |
| inHg | kPa | 3.38639 |
| mmHg (torr) | kPa | 0.133322 |
Tires and Everyday Uses
Passenger car tires are commonly inflated to 30 to 36 PSI (2.1 to 2.5 bar), and the recommended value is on a placard inside the driver's door and not on the tire sidewall, which shows the maximum. Bicycle road tires run 80 to 120 PSI (5.5 to 8.3 bar), mountain bike tires 25 to 35 PSI (1.7 to 2.4 bar). A pressure washer might deliver 2,000 PSI (138 bar). Home water pressure is typically 40 to 80 PSI (2.8 to 5.5 bar). A scuba tank is filled to about 3,000 PSI (207 bar).
Check tire pressure when tires are cold, because driving warms the air and raises the reading by 2 to 4 PSI.
Gauge vs. Absolute Pressure
Most gauges read gauge pressure, the difference from the surrounding atmosphere. A tire gauge reading 32 PSI means 32 PSI above the atmosphere, so the absolute pressure inside is about 32 + 14.7 = 46.7 PSI. Absolute pressure is zero in a perfect vacuum, while gauge pressure is zero at atmospheric pressure. In gas law calculations, always use absolute pressure. Units are often labeled PSIG (gauge) or PSIA (absolute).
A vacuum gauge reads negative gauge pressure. A reading of −10 PSIG means an absolute pressure of about 4.7 PSIA.
Weather and Aviation Pressure
Standard sea-level pressure is 1,013.25 hectopascals (hPa), the same as millibars (mb), or 29.92 inches of mercury. Low-pressure weather systems may be 980 to 1,000 hPa and strong highs 1,030 to 1,040 hPa. Pressure falls with altitude by about 12 hPa per 100 meters near sea level: at 3,000 meters, it is about 700 hPa, roughly 70% of sea-level pressure. Aircraft altimeters rely on this relationship. Hurricanes can have central pressures below 920 hPa.
Practical Tips
Buy a good-quality gauge and check your tires monthly. Use the unit your gauge shows, but convert carefully when following instructions in another unit. Remember that a 1 bar difference is large: the difference between 2.0 bar and 3.0 bar is 14.5 PSI, which would make a car tire dangerously over- or underinflated.
Frequently Asked Questions
How many PSI is 1 bar?
14.5038 PSI.
What is 32 PSI in bar?
About 2.21 bar.
What is the difference between gauge and absolute pressure?
Gauge pressure is measured relative to atmospheric pressure, while absolute pressure is relative to a vacuum.
What is standard atmospheric pressure?
101.325 kPa, which is 14.696 PSI or 1,013.25 hPa.
Why does tire pressure rise when I drive?
Heat from friction warms the air, which raises its pressure.