PSI vs Bar: Pressure Units Compared
Key Difference
1 bar = 14.5038 PSI. Bar is a metric-derived unit roughly equal to atmospheric pressure at sea level. PSI (pounds per square inch) is an imperial unit widely used in the US for tire pressure, hydraulics, and compressed gases.
Side-by-Side Comparison
| Property | PSI | Bar |
|---|---|---|
| Full name | Pounds per square inch | Bar |
| Symbol | psi | bar |
| System | Imperial / US Customary | Metric-compatible (non-SI) |
| Used in | USA, UK (some applications) | Europe, Asia, most of the world |
| Common uses | Tire pressure, hydraulics, HVAC, scuba | Tire pressure, weather, industrial |
| Atmospheric pressure | 14.696 psi | 1.01325 bar |
| Conversion | 1 psi = 0.0689476 bar | 1 bar = 14.5038 psi |
Where Each Is Used
PSI dominates in the United States across nearly all pressure applications: car and bicycle tire pressure, air compressors, fire sprinkler systems, water pressure, and natural gas delivery. The UK also uses PSI for tire pressure, though other pressure applications increasingly use bar.
Bar is the standard in continental Europe and most of Asia. European tire pressure specifications, weather maps (using millibar or hectopascal, which are equivalent), industrial hydraulics, and scuba diving equipment all use bar. Many international automotive manufacturers specify tire pressure in bar.
In scientific contexts, the SI unit is the pascal (Pa), with 1 bar = 100,000 Pa. However, bar remains popular in engineering because it is close to 1 atmosphere, making it intuitive for practical applications.
Conversion Formulas
PSI to Bar
bar = psi × 0.0689476
Example: 32 psi = 32 × 0.0689476 = 2.206 bar
Bar to PSI
psi = bar × 14.5038
Example: 2.2 bar = 2.2 × 14.5038 = 31.91 psi
Quick Reference Table
| Application | PSI | Bar |
|---|---|---|
| Standard atmosphere | 14.696 | 1.013 |
| Bicycle tire (road) | 80-130 | 5.5-9.0 |
| Car tire (typical) | 30-35 | 2.1-2.4 |
| Truck tire | 80-100 | 5.5-6.9 |
| Home water pressure | 40-80 | 2.8-5.5 |
| Scuba tank | 3,000 | 207 |
| Espresso machine | 130-135 | 9.0-9.3 |
When to Use Which
Use PSI when working with American equipment, following US tire pressure specifications, or communicating with US-based colleagues. Most American-made air compressors, pressure washers, and HVAC systems use PSI exclusively.
Use bar when working with European or Asian equipment, reading international automotive specifications, or in any scientific or engineering context outside the US. European-made espresso machines, compressors, and hydraulic systems are rated in bar.
A quick mental shortcut: divide PSI by 15 to get an approximate bar value, or multiply bar by 15 to get approximate PSI. This is within 3% accuracy, close enough for everyday estimates.
A Brief History
PSI emerged naturally from the imperial system. As engineers needed to quantify pressure, they described it in terms of the units they already used: pounds of force distributed over a square inch of area. The unit has been in widespread use since the industrial revolution, particularly in steam engine engineering.
Bar was introduced by the British meteorologist Napier Shaw in 1909. The name comes from the Greek word “baros,” meaning weight. It was designed so that 1 bar would be close to standard atmospheric pressure, making it intuitive for weather and industrial use. Although not an official SI unit, it is accepted for use with SI and is defined as exactly 100,000 pascals.