Definition-controlled unit arithmetic
Defined Pressure-Unit Converter
Convert one declared pressure quantity through pascals. Absolute, gauge and differential pressure use the same unit factors, but they are different reference quantities and are never changed into one another here.
Defined-unit conversions
One multiplicative conversion
xārā = pPa / fārā
f = pascals represented by one named unit
This changes only the numerical unit representation. It does not change the physical pressure reference, measurement location, timestamp, direction convention, uncertainty or significant figures of the source measurement.
Absolute, gauge and differential are not unit names
That equation is a separate physical reference conversion, not a unit conversion. Use the actual absolute ambient pressure applicable at the same place and time. Do not insert the standard atmosphere of 101325 Pa unless it really is the specified reference. Differential pressure also needs an explicit high-minus-low or opposite sign convention.
Exact defined routes
| Unit key | Definition used | Statuss |
|---|---|---|
| Pa | 1 Pa | SI coherent derived unit |
| kPa | 1000 Pa | Exact SI prefix |
| MPa | 1000000 Pa | Exact SI prefix |
| bārs | 100000 Pa | Exact |
| mbar | 100 Pa | Exact decimal submultiple of bar |
| psi | 4.4482216152605 N / (0.0254 m)² = 6894.757293168361 Pa | Exact international inch and standard-gravity pound-force basis |
| atm | 101325 Pa | Exact standard atmosphere |
| at = kgf/cm² | 98066.5 Pa | Exact technical atmosphere on standard gravity |
| Torr | 101325/760 Pa | Exact |
NIST-tabulated manometer routes
| Qualified unit | Factor used | Why qualification matters |
|---|---|---|
| conventional mmHg | 133.3224 Pa | Separate from Torr |
| conventional inHg | 3386.389 Pa | Conventional definition |
| inHg at 32 °F | 3386.38 Pa | Mercury density at stated temperature |
| inHg at 60 °F | 3376.85 Pa | Mercury density at stated temperature |
| conventional mmH₂O | 9.80665 Pa | Conventional definition |
| mmH₂O at 4 °C | 9.80638 Pa | Water density at stated temperature |
| conventional inH₂O | 249.0889 Pa | Conventional definition |
| inH₂O at 39.2 °F | 249.082 Pa | Water density at stated temperature |
| inH₂O at 60 °F | 248.84 Pa | Water density at stated temperature |
NIST notes that temperature-specific manometer factors use standard gravity and the fluid density at the stated temperature; additional digits are not justified because of fluid compressibility and temperature-scale effects. Results involving these tabulated factors therefore must not be presented as exact beyond their source precision.
BIPM SI Brochure
Portāls BIPM SI Brochure, 9th edition, version 4.01 (June 2026) is the current authoritative SI description. It identifies the pascal as the SI pressure unit through SI mechanics and lists bar as exactly 0.1 MPa = 100000 Pa. Non-SI routes on this page are conversion conveniences, not SI units merely because they can be expressed in pascals.
NIST SP 811
NIST SP 811 Appendix B.9 supplies the pressure factors and explicitly distinguishes conventional, 32 °F, 60 °F, 4 °C and 39.2 °F manometer units. Footnote 12 explains the density/temperature and precision boundary. NIST Chapter 5 gives 1 Torr = 101325/760 Pa and 1 atm = 101325 Pa. Sources accessed 13 July 2026.
No ISO pressure-conversion formula or conformity statement is claimed. If a contract, calibration certificate, code or instrument manual uses an unqualified column unit differently, its controlled definition and uncertainty take precedence.
