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Pressure Conversion Overview
The Pressure Conversion tool converts pressure values between common engineering, laboratory, HVAC, hydraulic, pneumatic, meteorological, and vacuum units. Enter a value in one unit and the calculator displays the equivalent pressure in the other supported units.
Supported units include pascal, kilopascal, megapascal, bar, psi, psf, atmosphere, torr, millimeter of mercury, inch of mercury, millimeter of water column, inch of water column, and kilogram-force per square centimeter.
What Is Pressure?
Pressure is force applied perpendicular to a surface divided by the area over which that force is applied.
Pressure = Force / Area
The SI unit of pressure is the pascal. One pascal equals one newton per square meter:
1 Pa = 1 N/m²
Common Pressure Units
| Unit | Symbol | Equivalent in Pascals | Common Use |
|---|---|---|---|
| pascal | Pa | 1 Pa | SI pressure unit, scientific and engineering calculations. |
| kilopascal | kPa | 1000 Pa | General engineering, HVAC, tire pressure in some regions. |
| megapascal | MPa | 1000000 Pa | Hydraulics, materials, high-pressure systems. |
| bar | bar | 100000 Pa | Industrial pressure, compressors, pneumatics. |
| standard atmosphere | atm | 101325 Pa | Reference atmospheric pressure. |
| pound per square inch | psi | 6894.757 Pa | Tires, hydraulics, compressed air, US customary systems. |
| torr | Torr | 133.322 Pa | Vacuum measurement and laboratory pressure. |
| millimeter of mercury | mmHg | 133.322 Pa | Blood pressure, vacuum, barometric pressure. |
| inch of mercury | inHg | 3386.389 Pa | Weather, aviation, vacuum gauges. |
| inch of water column | inH2O | 249.089 Pa | HVAC, low-pressure gas systems, airflow measurement. |
Pressure Unit Conversion Formula
Most pressure conversions can be handled by converting the input value to pascals first, then converting from pascals to the desired output unit.
Value in Pa = Input Value × Unit Factor
Output Value = Value in Pa / Output Unit Factor
For example, because 1 psi = 6894.757 Pa:
30 psi = 30 × 6894.757 Pa = 206842.71 Pa = 206.843 kPa
Example Conversions
| Input | Conversion | Result |
|---|---|---|
| 1 bar | 1 bar = 100000 Pa | 100 kPa |
| 1 atm | 1 atm = 101325 Pa | 101.325 kPa |
| 14.6959 psi | 14.6959 psi ≈ 101325 Pa | 1 atm |
| 760 Torr | 760 Torr = 101325 Pa | 1 atm |
| 100 inH2O | 100 × 249.089 Pa | 24.909 kPa |
How to Use the Pressure Conversion Tool
Enter the pressure value in the unit you already know. The calculator converts the value into equivalent pressure values across the available units. Use enough significant digits for engineering work, especially when converting calibration values, sensor ranges, or safety limits.
If the result will be used for equipment selection, compare the converted value with the sensor datasheet, valve rating, gauge range, pipe rating, or applicable safety code. Unit conversion does not replace pressure-system design review.
Absolute, Gauge, and Differential Pressure
| Pressure Type | Meaning | Example Label |
|---|---|---|
| Absolute pressure | Measured relative to a perfect vacuum. | psia, kPa absolute |
| Gauge pressure | Measured relative to local atmospheric pressure. | psig, bar gauge |
| Differential pressure | Measured as the difference between two pressure points. | psid, Pa differential |
Unit conversion changes the unit, not the pressure reference. For example, converting 30 psig to kPa gives a gauge pressure in kPa, not an absolute pressure. To convert between gauge and absolute pressure, you must account for local atmospheric pressure.
Water Column and Mercury Column Units
Units such as mmH2O, inH2O, mmHg, and inHg come from manometer measurements. They express pressure as the height of a liquid column. These units depend on reference density and gravity assumptions, so high-accuracy work should use the exact standard or calibration reference required by the application.
Water column units are often used for low pressure in HVAC and gas systems. Mercury column units are common in barometry, vacuum measurement, and medical pressure measurement.
Common Mistakes to Avoid
| Mistake | Correct Approach |
|---|---|
| Confusing psi and psf. | psi is pound-force per square inch; psf is pound-force per square foot. |
| Mixing gauge and absolute pressure. | Keep the same reference type unless you intentionally add or subtract atmospheric pressure. |
| Rounding too early. | Keep enough significant digits during intermediate conversions. |
| Assuming water-column units are universal constants. | Check the temperature and density reference for precision calibration work. |
| Using conversion results as equipment ratings. | Always check manufacturer ratings and safety factors. |
Applications
Pressure conversion is used in pneumatic systems, hydraulic systems, vacuum systems, compressors, HVAC, barometers, weather data, tire pressure, medical devices, industrial sensors, process control, gas regulators, and laboratory measurement.
The most common engineering workflow is to convert a sensor range or specification into the unit used by the rest of the design. For example, a pressure transducer may be rated in psi, while the controller expects kPa or bar.
FAQ
What is the SI unit of pressure?
The SI unit of pressure is the pascal, symbol Pa. One pascal equals one newton per square meter.
Is bar the same as atmosphere?
No. One bar is exactly 100000 Pa. One standard atmosphere is 101325 Pa, so one atmosphere is slightly higher than one bar.
Why are psi and kPa both used?
psi is common in US customary applications, while kPa is a metric unit used in many engineering and scientific contexts. The calculator converts between them.
Can I convert gauge pressure to absolute pressure with this tool?
The tool converts units. To convert gauge pressure to absolute pressure, add the local atmospheric pressure first, then convert units if needed.
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