Pressure Unit Converter: psi, bar, kPa, MPa, atm, mmHg

Pressure shows up in oilfield, construction, and general engineering work in at least six different units depending on region, discipline, and equipment vintage: psi, bar, kilopascals, megapascals, atmospheres, and millimeters of mercury. This converter switches instantly between all six so a casing burst rating, a wellhead pressure reading, or a regulatory limit can be compared no matter which unit it was originally written in.

Conversion factors

Every unit converts through pascals as a common base. One atmosphere, the reference pressure of the Earth’s atmosphere at sea level, equals each of the following:

• 14.696 psi (pounds per square inch)
• 1.01325 bar
• 101.325 kPa (kilopascals)
• 0.101325 MPa (megapascals)
• 760.0 mmHg (millimeters of mercury)

To convert any value, multiply it by its unit’s factor in pascals, then divide by the target unit’s factor. The calculator above does this automatically and shows all six units at once.

Worked example

Consider a wellhead shut-in pressure of 5,000 psi, a typical high pressure surface reading.

1. Pressure in pascals = 5,000 times 6,894.757 = 34,473,785 Pa
2. Bar = 34,473,785 / 100,000 = 344.738 bar
3. kPa = 34,473,785 / 1,000 = 34,473.8 kPa
4. MPa = 34,473,785 / 1,000,000 = 34.474 MPa
5. atm = 34,473,785 / 101,325 = 340.230 atm

These are the exact numbers the calculator returns when you click Load Example, so you can confirm the tool matches a hand calculation before relying on it for a real pressure comparison.

Where each unit is used

Psi dominates oilfield pressure reporting in North America, from wellhead pressure gauges to casing burst and collapse ratings. Bar and kPa are the standard almost everywhere else, including most international drilling contractors and equipment manufactured in Europe or Asia. MPa appears frequently in casing and tubing specification sheets and structural engineering codes. Atmospheres serve as a simple reference point for comparing a pressure against normal atmospheric conditions, and mmHg remains the traditional unit for vacuum service and barometric readings.

Common mistakes

• Confusing bar and atm, which are close but not identical (1 bar = 0.9869 atm), a small error that compounds across a long pressure profile
• Mixing up gauge pressure and absolute pressure when converting a reading that already includes atmospheric pressure
• Applying the wrong significant figures when converting a high precision equipment rating, since psi to MPa conversions can lose apparent precision if rounded too early

A quick word of caution on mmHg and atm: they show up constantly in older textbooks and lab equipment but rarely on field pressure gauges, which almost always read psi, bar, or kPa depending on where the equipment was manufactured. If you are cross checking a wellhead reading against a spec sheet from a different country, double check which unit the spec was actually written in before assuming the numbers do not match. More unit mismatches get blamed on faulty gauges than actually are faulty gauges.

Popular pressure conversions

The pressure values people look up most often. Each opens the converter on that figure with its own address you can bookmark or share.

Related Calculator and Reference

See also the Bearing Pressure Converter for ground bearing units specifically, including tsf, ksf and kg per square centimetre. The general purpose Pressure Converter covers psi, bar, kPa, MPa, atm, mmHg and water head with gauge and absolute counterparts and a live gauge dial.

For casing pressure ratings that use these same units, see the Casing Burst Pressure Calculator. For the official SI definition of the pascal and related pressure units, see the NIST SI Units: Pressure reference.