Conversion Basis
All conversions are anchored to the canonical bar. Every unit simply expresses the same physical pressure, so the engine first normalises the input value into bar and then into the requested target unit:
X = P × (b/P_from_unit) × (P_to_unit/b) Where:
-
P= Pressure value to convert [varies by unit] -
b= Canonical base value in bar (1 bar = 10⁵ Pa) [bar] -
X= Converted value in the target unit [target unit]
Derived Equations:
1 bar = 100 kPa = 0.1 MPa 1 bar = 14.5038 psi = 0.98692 atm 1 bar = 10.1972 m H₂O = 33.455 ft H₂O How the Calculation Works
Each supported unit stores a fixed factor relative to the bar, drawn from the SI-derived set below (g = 9.80665 m/s², ρ = 1000 kg/m³ for the water-column terms):
bar = 1 · kPa = 0.01 · MPa = 10 · psi = 1/14.5038 · atm = 1/0.98692 · m H₂O = 1/10.1972
Values are first divided by their own factor to recover the pressure in bar, then multiplied by the target unit’s factor. Results are reported with engineering formatting plus a visual note confirming the conversion relationship.
Worked Engineering Example
Design Scenario: Translate a 1 bar Pump Discharge into PSI
- Normalise to bar:
P(bar) = 1 × 1 = 1.00 bar - Convert to psi:
1 bar = 1 / (1/14.5038) = 14.5038 psi - Check with water head (gauge):
1 bar = 10.1972 m H₂O = 33.455 ft H₂O = 0.98692 atm - Scale check:
5 bar = 72.52 psi = 0.5 MPa = 50.99 m H₂O
Engineering Notes & Design Benchmarks
| Unit Pairs | Factor | Common Use |
|---|---|---|
| bar ↔ psi | 1 bar = 14.5038 psi | Pump curves (EU vs. US equipment) |
| bar ↔ kPa | 1 bar = 100 kPa | SI system design and codes |
| m H₂O ↔ bar | 10.1972 m = 1 bar | Pump head / static elevation checks |
| MPa ↔ kPa | 1 MPa = 1000 kPa | High-pressure pipelines & structural |
Water-column conversions assume fresh water at ρ = 1000 kg/m³ (4 °C). For brine, slurries, or elevated-temperature water the head-to-pressure factor must scale with the actual density: P(ρ) = P_water × ρ/1000.
Assumptions & Limitations
- Water-column units use g = 9.80665 m/s² and ρ = 1000 kg/m³ exactly.
- All values are absolute or gauge as supplied; the converter does not add atmospheric pressure.
- Rounding follows engineering convention — full precision is retained internally, then formatted for display.
Frequently Asked Questions
Why does 1 bar equal about 10.2 m of water?
Because the pressure of a water column is ρgh. At ρ = 1000 kg/m³ and g = 9.80665 m/s², a 1 bar (10⁵ Pa) pressure corresponds to h = 10⁵/(1000 × 9.80665) = 10.1972 m of water.
Is "m H₂O" different from "head"?
No — metres of water column is exactly pump head expressed as a pressure. That is why pump curves drawn in metres can be converted to bar by dividing by 10.1972.
Does temperature affect these conversions?
Only the water-column units, through density. The pressure unit factors themselves (bar, psi, kPa, atm) are exact. If your fluid density differs from 1000 kg/m³, scale the water-column result by ρ/1000.
Engineering Disclaimer
Engineering Note: This converter applies exact unit factors and density-normalized water-column terms for design documentation. Always re-verify pressure conventions with regional codes before releasing calculations.
Technical References
- SI Brochure: The International System of Units, 9th ed., BIPM, 2019.
- NIST, Guide for the Use of the International System of Units (SP 811), 2008.
- ISO 4126 / ASME standards, pressure measurement and unit conventions.