Pressure unit conversion
Converts pressure between pascals, kilopascals, bar, PSI, atmospheres, and millimeters of mercury (mmHg). These units turn up in very different contexts - tire pressure is usually in PSI or bar, weather reports use hectopascals, and medical blood pressure readings use mmHg - so this tool lets you move between them without memorizing the conversion factors.
Why so many different units exist for the same physical quantity
Each unit developed within a specific industry or scientific tradition - PSI (pounds per square inch) comes from imperial engineering and is standard for tires and hydraulics in the US, bar and pascals are the metric standard used in most of the world and in scientific contexts, and mmHg persisted in medicine because mercury-column manometers were the original blood pressure measuring instrument, with the unit surviving long after digital devices replaced the mercury itself.
Why atmospheres make a useful reference point
One atmosphere (atm) represents standard sea-level air pressure, which makes it a useful intuitive reference - a pressure reading well above 1 atm (like a car tire, typically 2+ bar) is easy to contextualize against the everyday air pressure you're used to, rather than just looking at an abstract pascal or PSI number.
Getting your tire pressure right across unit systems
Many vehicle manuals and tire sidewalls list the recommended pressure in PSI, while some pumps and gauges (especially outside the US) display bar or kPa - converting correctly between whichever unit your gauge uses and whichever unit your manual specifies matters directly for safety and tire wear, not just as an abstract conversion exercise.