Pressure Unit Conversion: A Complete Guide
Pressure appears in more everyday situations than most people realise. Tyre pressure, blood pressure, weather forecasts, plumbing systems, cooking with a pressure cooker, scuba diving and industrial machinery all involve pressure measurements in one form or another.
The challenge is that different industries and countries use different pressure units. This guide explains the most common units, shows you how to convert between them and links to the free Pressure Converter for instant calculations.
The Main Pressure Units
| Pascal (Pa) | The SI unit of pressure. Equal to one newton per square metre. Very small on its own so kilopascal (kPa) is commonly used. |
| Kilopascal (kPa) | 1,000 pascals. Used in weather forecasting and vehicle tyre pressure in many countries. |
| Bar | Approximately equal to atmospheric pressure at sea level. Used in weather, meteorology and industrial systems. |
| Millibar (mbar) | One thousandth of a bar. Used in weather forecasting for atmospheric pressure readings. |
| PSI (pounds per square inch) | Used in the US for tyre pressure, plumbing and industrial applications. |
| Atmosphere (atm) | Defined as standard sea level atmospheric pressure. Used in chemistry and diving. |
| Torr / mmHg | Used in medicine and vacuum science. 1 Torr = 1 mmHg = 133.322 Pa. |
Key Conversion Factors
Core Pressure Conversions
1 bar = 100,000 Pa = 100 kPa = 14.504 PSI = 0.9869 atm
1 PSI = 6,894.76 Pa = 6.895 kPa = 0.0689 bar = 0.0680 atm
1 atm = 101,325 Pa = 101.325 kPa = 1.01325 bar = 14.696 PSI
1 kPa = 1,000 Pa = 0.01 bar = 0.145 PSI
Tyre Pressure Quick Reference
32 PSI = 2.206 bar = 220.6 kPa
35 PSI = 2.413 bar = 241.3 kPa
Pressure Conversion Reference Table
| From | Kilopascal (kPa) | PSI |
|---|---|---|
| 1 Pa | 0.001 kPa | 0.000145 PSI |
| 1 kPa | 1 kPa | 0.145 PSI |
| 1 bar | 100 kPa | 14.504 PSI |
| 1 PSI | 6.895 kPa | 0.069 bar |
| 1 atm | 101.325 kPa | 14.696 PSI |
| 1 Torr / mmHg | 0.133 kPa | 0.01934 PSI |
Tyre Pressure: PSI vs Bar vs kPa
| PSI | Bar | kPa |
|---|---|---|
| 26 PSI | 1.79 bar | 179 kPa |
| 28 PSI | 1.93 bar | 193 kPa |
| 30 PSI | 2.07 bar | 207 kPa |
| 32 PSI | 2.21 bar | 221 kPa |
| 35 PSI | 2.41 bar | 241 kPa |
| 38 PSI | 2.62 bar | 262 kPa |
| 40 PSI | 2.76 bar | 276 kPa |
| 44 PSI | 3.03 bar | 303 kPa |
Most passenger car tyres are inflated to between 30 and 35 PSI. SUVs and trucks are often higher. Always check your vehicle door sticker or handbook for the correct pressure for your specific vehicle.
Blood Pressure: mmHg
Blood pressure is measured in millimetres of mercury (mmHg), a legacy unit from the mercury column sphygmomanometers historically used in medicine. It is still used universally in medicine today.
| Normal blood pressure | Below 120/80 mmHg |
| Elevated blood pressure | 120 to 129 systolic / below 80 diastolic mmHg |
| High blood pressure stage 1 | 130 to 139 systolic / 80 to 89 diastolic mmHg |
| High blood pressure stage 2 | 140 or above systolic / 90 or above diastolic mmHg |
| Hypertensive crisis | Above 180 systolic and/or above 120 diastolic mmHg |
Atmospheric Pressure and Weather
Standard sea level atmospheric pressure is 1,013.25 mbar (millibars), or equivalently 101.325 kPa, or 1 atm. Weather reports usually express pressure in millibars or hectopascals (hPa), which are numerically identical to millibars.
- High pressure (above 1020 mbar) generally brings settled, dry weather
- Low pressure (below 1000 mbar) generally brings unsettled, rainy weather
- A very deep low pressure storm can drop to 960 mbar or below
Related Tools
- Pressure Converter PSI, bar, pascal, kPa, atm, Torr and more
- All Unit Converters browse all 74 converters on CalConvs
Frequently Asked Questions
What is the correct tyre pressure in bar and PSI?
Most passenger cars run between 30 and 35 PSI (2.07 to 2.41 bar, or 207 to 241 kPa). The exact recommended pressure for your vehicle is printed on a sticker inside the driver's door or in the vehicle handbook. Under-inflated tyres reduce fuel economy and increase tyre wear. Over-inflated tyres reduce grip and ride comfort. Always check pressure when the tyres are cold.
What is the difference between PSI and bar?
PSI stands for pounds per square inch, a pressure of one pound-force applied over one square inch of area. Bar is a metric unit equal to 100,000 pascals, approximately equal to atmospheric pressure at sea level. To convert PSI to bar, divide by 14.5038. To convert bar to PSI, multiply by 14.5038. Both measure the same thing but are used in different industries and countries.
What is normal atmospheric pressure in kPa?
Standard atmospheric pressure at sea level is 101.325 kPa (kilopascals), which is also 1 atm, 1013.25 mbar, or 14.696 PSI. Atmospheric pressure decreases with altitude, at the top of Mount Everest, pressure is about 33.7 kPa, roughly one third of sea level pressure.
Why is blood pressure measured in mmHg?
Blood pressure is measured in millimetres of mercury (mmHg) because early blood pressure gauges used a column of mercury to measure pressure, the higher the pressure, the higher the mercury was pushed. Although modern devices are electronic, the mmHg unit is retained for historical continuity and because all blood pressure guidelines are written in these units. 1 mmHg equals 133.322 pascals.