Pressure Converter
Convert pressure between pascals, kilopascals, megapascals, bar, psi, atmospheres, and mmHg.
How to use this tool
- Enter pressure and from unit in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your psi and the full breakdown beneath it.
Formula
All units convert to pascals (Pa) first, then to the target unit:
Pa = input × factorfrom
output = Pa ÷ factorto
Key factors: Pa = 1 | kPa = 1000 Pa | MPa = 1,000,000 Pa | bar = 100,000 Pa | psi = 6894.757 Pa | atm = 101,325 Pa | mmHg = 133.322 Pa
How it works
The pascal (N/m²) is the SI unit of pressure. The converter normalises input to pascals using the appropriate factor, then divides by each output unit's pascal equivalent. The atmosphere (101,325 Pa) and bar (100,000 Pa) are closely related but not identical — standard atmosphere is 1.01325 bar.
A common mistake is conflating bar and atmosphere: they differ by about 1.3%, which is negligible in casual contexts but significant in precision engineering, diving decompression tables, or gas-law calculations. Using 1 bar ≈ 1 atm without accounting for the difference can introduce meaningful errors in safety-critical applications.
Worked example
Convert 1 bar to all pressure units
- Input: 1 bar (from_unit = bar), so base in pascals = 1 × 100,000 = 100,000 Pa.
- kPa: 100,000 / 1000 = 100 kPa. MPa: 100,000 / 1,000,000 = 0.1 MPa.
- PSI: 100,000 / 6894.757 ≈ 14.5038 psi.
- Atmospheres: 100,000 / 101,325 ≈ 0.9869 atm. mmHg: 100,000 / 133.322 ≈ 750.062 mmHg.
100,000 Pa | 100 kPa | 0.1 MPa | 1 bar | 14.5038 psi | 0.9869 atm | 750.062 mmHg
Common mistakes to avoid
- Confusing psi (pound-force per square inch) with kPa when reading tire pressure -- a typical car tire at 32 psi is about 220 kPa, not 32 kPa.
- Treating 1 atm and 1 bar as identical -- 1 atm = 101,325 Pa while 1 bar = 100,000 Pa; the 1.3% difference matters in precision gas law calculations.
- Forgetting that mmHg is a gauge concept from a mercury column -- 760 mmHg = 1 atm at standard conditions, but partial-pressure problems require consistent absolute units.
Key terms
- Pascal (Pa)
- The SI unit of pressure, equal to one newton per square metre. Named after Blaise Pascal.
- PSI (pounds per square inch)
- An imperial pressure unit equal to 6894.757 Pa, commonly used for tyre pressure, hydraulics, and gas cylinders in the US.
- Atmosphere (atm)
- A reference pressure unit equal to 101,325 Pa, defined as the mean atmospheric pressure at sea level.
- mmHg (millimetre of mercury)
- A pressure unit equal to 133.322 Pa, defined by the pressure exerted by a 1 mm column of mercury. Still used in blood pressure and meteorology.
Frequently asked questions
- What is the difference between gauge pressure and absolute pressure?
- Absolute pressure is measured from true zero (vacuum). Gauge pressure is measured relative to ambient atmospheric pressure. Tire pressure gauges read gauge pressure, so a reading of 32 psi means 32 psi above atmosphere, or about 46.7 psi absolute.
- How many psi is 1 bar?
- 1 bar = 14.5038 psi. Many European car manuals give tire pressure in bar; 2.2 bar is roughly 32 psi.
- Why is blood pressure measured in mmHg?
- Early blood pressure devices used mercury manometers, and the convention of reporting in millimetres of mercury (mmHg) persisted even after electronic sensors replaced mercury. A normal reading of 120/80 mmHg corresponds to about 16.0/10.7 kPa.