Pressure Conversions
Convert pressure units instantly: pascal (Pa), kilopascal (kPa), bar, millibar, psi, atmospheres, torr, mmHg, inHg, inH2O, and kg/cm2. Engineering, lab, HVAC, and weather-friendly pressure converter with formulas and tables.
Conversion inputs
Enter a value and select the units you are converting from and to. Filters limit choices to the most relevant groups.
Quick table: psi ↔ bar ↔ kPa
| psi | bar | kPa | Notes |
|---|---|---|---|
| 1 | 0 | 0 | Tyre low range |
| 14.5 | 0 | 0 | ≈ 1 bar |
| 29 | 0 | 0 | Car tyres mid |
| 145 | 0 | 0 | Hydraulic, test |
Base definitions: 1 atm = 101325 Pa; 1 bar = 100000 Pa; 1 mbar = 100 Pa; 1 psi = 6894.757 Pa; 1 torr = 133.322368 Pa; 1 mmHg = 133.322368 Pa; 1 inHg = 3386.389 Pa; 1 inH2O = 249.0889 Pa; 1 kg/cm2 = 98066.5 Pa.
How to Use This Converter
Choose the source value and unit, then select the destination unit. The converter always routes through the pascal (Pa) as the base unit, so the math stays consistent across any measurement system.
Toggle the filters to surface only the units used in your workflow: common, weather/HVAC, vacuum/lab, or industrial.
Methodology
This calculator converts every unit to pascals first, then divides by the target unit factor. This two-step approach prevents rounding drift and mirrors lab-grade conversions.
Pa = value × factorToPa[sourceUnit]
target = Pa ÷ factorToPa[targetUnit]
Example: 25 psi → bar: 25 × 6894.757 = 172,368.925 Pa → 172,368.925 ÷ 100,000 = 1.7237 bar.
Common pressure units
- Pa / kPa / MPa: SI, engineering, hydraulics.
- bar / mbar: industry, weather, scuba.
- psi: US industry, tyres, hydraulics.
- atm: chemistry, thermodynamics.
- torr / mmHg: vacuum, lab instruments.
- inHg / inH2O: HVAC, weather, duct testing.
FAQ
1. Why are torr and mmHg the same here?
Modern practice often uses 1 torr = 133.322368 Pa, exactly matching 1 mmHg at 0 °C. For vacuum and lab work this is fine and keeps the tool simple.
2. Can I do gauge vs absolute here?
This page converts units directly (absolute-style). To convert gauge to absolute add ambient atmospheric pressure before converting.
3. Are these definitions NIST-compatible?
Yes, the constants above follow commonly published NIST/NMI values and are suitable for engineering calculators.
Full original guide (expanded)
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Pressure tips
- HVAC often uses inH2O and BTU/hr elsewhere.
- Weather uses mbar (hPa) — they are the same number.
- State if your value is gauge (g) or absolute (abs).