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Pressure Converter
Convert between Pascal, Bar, PSI, and Atmosphere instantly. Understand tire pressure, weather forecasts, and engineering specs.
Why Pressure Has So Many Units
Pressure = Force ÷ Area. Different industries adopted different units because they work at different scales. Here's when to use each.
Common Pressure Units
- Pascal (Pa): SI unit. 1 Pa = 1 Newton per square meter. Too small for daily use (1 PSI = 6,895 Pa).
- Bar: 100,000 Pa. Used in Europe for tire pressure, weather (millibars), diving.
- PSI (lb/in²): US standard. Tires, air compressors, hydraulics.
- Atmosphere (atm): Reference standard = sea-level air pressure (101,325 Pa).
⚠️ Unit Mix-Up Warning
Never confuse PSI and Bar! A tire rated for 32 PSI (2.2 Bar) inflated to 32 Bar would explode (464 PSI). Always check your car's door sticker and use the right unit. European cars show Bar, US cars show PSI.
Real-World Pressure Examples
Car Tires: 32 PSI = 2.2 Bar = 220 kPa. Under-inflation by 20% (25 PSI) reduces fuel economy by 3% and tire life by 25%.
Weather Forecast: "Low pressure system" = ~1,000 millibars (1 Bar). "High pressure" = ~1,030 mbar. Just a 3% swing changes weather.
Scuba Diving: Every 10 meters deep adds 1 Bar of pressure. At 30m depth, you experience 4 Bar (1 atm air + 3 Bar water).
Espresso Machine: 9 Bar (130 PSI). Less than 7 Bar = weak, watery coffee. More than 11 Bar = over-extracted, bitter.
Mount Everest Summit: 0.33 atm (33 kPa, 4.9 PSI). Your lungs get 1/3 the oxygen. This is why climbers need supplemental O₂.
💡 Tire Pressure Tip
Check tire pressure when cold (before driving). Driving heats tires and increases pressure by ~4 PSI (0.3 Bar). The recommended pressure on your door sticker assumes cold tires. Inflating hot tires to the sticker value means they'll be under-inflated when cold.
Reviewed by Dr. Alex M.
Ph.D. in Mechanical Engineering
Expert in fluid mechanics and pressure systems.
Frequently Asked Questions
What is the difference between PSI and Bar?
PSI (pounds per square inch) is used in the US. Bar is used globally. 1 Bar = 14.50 PSI. Your car tire might say 32 PSI (US) or 2.2 Bar (Europe). They measure the same thing—force per unit area—just different scales.
What is atmospheric pressure at sea level?
At sea level, atmospheric pressure is approximately 1 atm = 101,325 Pa = 1.01325 Bar = 14.7 PSI = 760 mmHg (Torr). This is the weight of Earth's atmosphere pressing down on you. Pressure decreases ~12% per 1,000 meters of altitude.
Why do tire pressures differ between US and Europe?
US uses PSI, Europe uses Bar. It's just different units. A typical car tire: 32 PSI (US) = 2.2 Bar (Europe) = 220 kPa. Always check your car's sticker (usually on driver's door) and use the unit shown. Don't mix them—inflating to 32 Bar instead of 32 PSI would explode your tire!