How this calculator works
This converter covers the pressure units used in weather reports, tire gauges, engineering specifications and medical readings: pascals and their multiples, bar, psi, standard atmospheres, and mercury-column units (mmHg/torr and inHg).
Every unit here converts through pascals using an independently defined exact constant — 1 atm = 101,325 Pa, 1 psi = 6,894.757293168 Pa, 1 bar = 100,000 Pa, and 1 mmHg = 133.322387415 Pa. Because each of these is its own fixed-point definition rather than derived from the others, some 'obvious' round numbers from older textbooks (like '1 atm = 760 mmHg exactly') are now only approximately true — see the FAQ below.
How it converts
result = value × (pascals per from-unit) ÷ (pascals per to-unit)Exact anchors: 1 atm = 101,325 Pa · 1 bar = 100,000 Pa · 1 psi = 6,894.757293168 Pa · 1 mmHg = 133.322387415 Pa1 inHg is derived here as 25.4 × 1 mmHg (since 1 inch = 25.4 mm exactly), giving 3,386.38864034 Pa.
Worked example: 32 psi to bar
- 32 psi × 6,894.757293168 Pa/psi = 220,632.23 Pa.
- 220,632.23 Pa ÷ 100,000 Pa/bar = 2.2063 bar.
- So a tire at 32 psi holds about 2.21 bar, or about 2.18 atm.
Frequently asked questions
Is 1 atmosphere exactly 760 mmHg?
Almost, but not exactly with modern constants. Historically the atmosphere was defined as 760 mmHg. Today both atm (101,325 Pa) and mmHg (133.322387415 Pa, from a fixed mercury density and standard gravity) are independently defined exact SI values, and 101,325 ÷ 133.322387415 works out to about 759.9999, not precisely 760. The difference is about one part in ten million and irrelevant for any practical measurement.
What is the difference between mmHg and torr?
For everyday and most scientific purposes they are treated as the same thing and this calculator uses one value for both. A strict modern definition of the torr (1/760 atm = 133.3223684211 Pa) differs from the conventional millimeter of mercury (133.322387415 Pa) by about 0.14 parts per million, well under two parts in ten million.
Why does my tire pressure gauge read differently from atmospheric pressure?
Tire gauges usually read gauge pressure — pressure above the surrounding atmosphere — not absolute pressure. A gauge reading of 32 psi means about 32 psi above atmospheric (14.7 psi), so the absolute pressure inside the tire is closer to 46.7 psi.
What pressure units do weather reports use?
Meteorologists commonly report barometric pressure in hectopascals (1 hPa = 100 Pa, the same size as a millibar) or in inHg in the US. Standard sea-level pressure is 1,013.25 hPa, equal to 1 atm.
How do I convert psi to kPa?
Multiply the psi value by 6.894757293168, the exact kPa-per-psi factor (1 psi = 6.894757293168 kPa). The worked example's 32 psi, for instance, converts to 32 × 6.894757293168 ≈ 220.63 kPa, the same 220,632.23 Pa figure expressed in kilopascals instead of pascals.