Reading Pressure Right: How to Convert psi, bar, kPa, atm and mmHg Without Mistakes
By the Super Simple Digital Tools Team · Updated June 2026
Pressure shows up in everyday life under a confusing pile of names, partly because different industries and countries standardised on different units long before there was an agreed metric base. A car's door placard might say 32 psi, a European pump reads in bar, a weather app shows 1015 hPa, a scuba tank is stamped 200 bar, and a clinic records 120/80 mmHg. They all measure the same quantity, force per unit area, so any one of them can be turned into any other once you know what each unit is anchored to.
That anchor is the pascal, the SI unit equal to one newton spread over one square metre. A pascal is tiny in human terms, which is why you rarely see raw pascals outside science; everyday units bundle thousands or hundreds of thousands of them. The clean definitions make conversion exact: 1 kPa is 1,000 Pa, 1 bar is 100,000 Pa, 1 hPa is 100 Pa (and identical to 1 millibar), 1 atm is 101,325 Pa, 1 psi is about 6,894.76 Pa, and 1 mmHg is about 133.322 Pa. Convert your value to pascals first, then back out to whatever unit you need, and the maths always lines up.
The fastest way to build intuition is to memorise a few reference points around normal air pressure at sea level. One atmosphere is roughly 14.7 psi, just over 1 bar, about 1013 hPa, and 760 mmHg. So a tyre at 32 psi is carrying a bit more than two atmospheres of air, a 200-bar dive cylinder holds close to 2,900 psi, and a stormy 980 hPa low is only about 3% below normal sea-level pressure. These anchors let you eyeball whether a converted number is sensible before you trust it.
The most common real error is not the arithmetic but mixing up gauge and absolute pressure. Most tyre gauges, pump dials and dive gauges read gauge pressure, meaning pressure above the surrounding atmosphere. Units like atm and many scientific readings are absolute, meaning they include that roughly 14.7 psi of background air. If you convert a gauge psi reading and compare it to an absolute value, you can be a whole atmosphere off. When precision counts, confirm which baseline each number uses before converting.
For routine jobs, pick the unit your equipment expects and convert toward it rather than away. Inflating tyres? Convert the placard figure into whatever your pump shows and stop there. Logging a metric medical form? Take the mmHg reading straight to kPa. Comparing cylinder specs? Settle on bar or psi and keep everything in that one unit. Doing the conversion once, into the unit you will actually act on, removes the back-and-forth where rounding and unit confusion creep in.
- Remember the sea-level anchor set: 1 atm = 14.7 psi = 1.013 bar = 1013 hPa = 760 mmHg, and use it to sanity-check any result.
- Check whether your reading is gauge or absolute before comparing it with atm or scientific values; the difference is roughly one atmosphere (about 14.7 psi).
- For tyres, the quick mental factors are: psi to bar divide by 14.5, psi to kPa multiply by about 6.9; e.g. 32 psi is roughly 2.2 bar.
- Treat hPa and millibar as the same number on weather maps, but never confuse them with bar, which is 1000 times larger.