Basic Concepts of Pressure Unit Conversion
Pressure is the force acting perpendicularly on the surface of an object, and its calculation formula is P=F/S. The magnitude of pressure is related to the weight of the object and the force-bearing area. On a horizontal surface, pressure equals weight (F=G=mg), with the unit being newton (N).
Common pressure units in engineering include Pa (pascal), kPa, MPa, bar, psi, kilogram-force/square centimeter (kgf/cm²), as well as millimeter water column, millimeter mercury column, etc.
Detailed Explanation of Common Pressure Units
psi (pound-force per square inch)
PSI stands for Pounds per square inch. P represents pound, S represents square, and I represents inch. European and American countries customarily use psi as a pressure unit.
- 1 psi = 6.894757 kPa
- 1 psi = 0.0689476 bar
- 1 bar ≈ 14.5 psi
Kilogram-force/square centimeter (kgf/cm²)
In China, gas pressure is often described in "kilograms", with the unit being kgf/cm², which means one kilogram of force acting on one square centimeter. Note that "kilogram" here is a unit of force, not mass.
Other Pressure Units
In addition, there are Pa (pascal, 1 newton/square meter), kPa, MPa, bar, millimeter water column (mmH₂O), millimeter mercury column (mmHg), etc. Different industries and regions have different habits, and the choice should be made according to the scenario.
Pressure Unit Conversion Relationships
Common Approximate Conversions (Engineering Mnemonics)
Since the differences between units are small, for non-precise calculations, you can remember it this way:
- 1 bar = 1 atm = 1 kgf/cm² = 100 kPa = 0.1 MPa
Precise Conversion Formulas
For precise calculations, please refer to the following relationships:
- 1 standard atmosphere (atm) = 0.101325 MPa = 1.01325 bar = 101.325 kPa = 14.695949 psi
- 1 bar = 0.1 MPa = 100 kPa = 1.0197162 kgf/cm²
- 1 standard atmosphere = 760 mmHg = 76 cmHg = 10.336 mH₂O = 101325 N/m² (often taken as 1.01×10⁵ Pa in calculations)
- 1 dyne/square centimeter (dyn/cm²) = 0.1 Pa
- 1 torr (Torr) = 133.322 Pa
- 1 millimeter mercury column (mmHg) = 133.322 Pa
- 1 millimeter water column (mmH₂O) = 9.80665 Pa
- 1 engineering atmosphere = 98.0665 kPa
- 1 kPa = 0.145 psi = 0.0102 kgf/cm² = 0.0098 atm
- 1 psi = 6.895 kPa = 0.0703 kgf/cm² = 0.0689 bar = 0.068 atm
Pressure Unit Conversion Table
For quick reference, common unit conversions are summarized as follows:
| Unit | Pa | kPa | MPa | bar | psi | kgf/cm² | atm |
|---|---|---|---|---|---|---|---|
| 1 Pa | 1 | 0.001 | 1e-6 | 1e-5 | 0.000145 | 0.0000102 | 9.87e-6 |
| 1 kPa | 1000 | 1 | 0.001 | 0.01 | 0.145 | 0.0102 | 0.0098 |
| 1 MPa | 1e6 | 1000 | 1 | 10 | 145.038 | 10.197 | 9.869 |
| 1 bar | 1e5 | 100 | 0.1 | 1 | 14.5038 | 1.0197 | 0.9869 |
| 1 psi | 6894.76 | 6.89476 | 0.006895 | 0.0689476 | 1 | 0.070307 | 0.068046 |
| 1 kgf/cm² | 98066.5 | 98.0665 | 0.0980665 | 0.980665 | 14.2233 | 1 | 0.96784 |
| 1 atm | 101325 | 101.325 | 0.101325 | 1.01325 | 14.6959 | 1.03323 | 1 |
Summary and Recommendations
Pressure unit conversion is crucial in industrial instrument selection, procurement, and technical communication. It is recommended that engineers memorize the approximate relationship 1 bar ≈ 1 atm ≈ 1 kgf/cm² ≈ 0.1 MPa ≈ 14.5 psi, which can meet most daily estimation needs.
For precise calculations or international projects, be sure to use standard conversion factors and pay attention to unit consistency. Correctly understand the difference between pressure and mass to avoid confusing "kilogram-force" with "kilogram mass".