Pressure Converter

Pressure is force spread over an area. The SI unit is the pascal (Pa), one newton per square meter. A single pascal is tiny, so real pressures are quoted in kilopascals, bar, psi, or atmospheres depending on the field you’re in.

Key relationships:

• 1 kPa = 1,000 Pa
• 1 bar = 100,000 Pa
• 1 psi = 6,894.76 Pa
• 1 atm = 101,325 Pa
• 1 mmHg = 133.322 Pa
• 1 mbar = 100 Pa (identical to 1 hPa, which is what forecasters now write)
• 1 inHg = 3,386.39 Pa

Worth memorizing:

• Standard atmosphere: 1 atm = 101,325 Pa = 1.013 bar = 14.7 psi = 760 mmHg = 1,013.25 mbar = 29.92 inHg
• A car tire: about 32 psi (≈ 2.2 bar / 220 kPa)

So many units survive because industries standardized separately. Weather uses millibars and inches of mercury, tires and plumbing use psi, science uses pascals, and diving and medicine use bar and mmHg. Converting between them is just the daily reality of each field.

A note on the weather units, since they cause the most head-scratching. The millibar and the hectopascal are the same size, exactly 100 Pa, so a chart reading 1013 mb and one reading 1013 hPa say precisely the same thing. Meteorology renamed the unit in the 1980s and kept the numbers identical on purpose, so nobody had to relearn what a normal reading looks like. American forecasters kept inches of mercury instead, where the same normal reading is 29.92.

The trap to watch is gauge versus absolute pressure. A tire gauge reads zero on a flat tire, because it measures pressure above the surrounding air. Absolute pressure counts up from a true vacuum, so a “32 psi” tire is really about 47 psi absolute once you add the atmosphere pressing on everything. For tires and weather the gauge value is what’s meant, but gas-law calculations almost always need the absolute figure. The converter shows both readings for whatever you type, so you never have to remember which one a formula wants.