Bar to PSI Converter
The bar is a metric pressure unit defined as exactly 100,000 pascals (100 kPa or 0.1 MPa). It is not an official SI unit but is legally recognized for use with the SI system across...
Formula
Source: Engineering Toolbox | Last reviewed: June 7, 2026
Examples
1 bar
= 14.5 psi
1 bar = 14.5 psi
5 bar
= 72.52 psi
10 bar
= 145 psi
100 bar
= 1450 psi
Quick Reference Table
| bar | psi |
|---|---|
| 1 | 14.5 |
| 2 | 29.01 |
| 5 | 72.52 |
| 10 | 145.04 |
| 50 | 725.19 |
| 100 | 1450.38 |
Where is this used?
Process engineers working on EPC projects in the Middle East or Southeast Asia routinely encounter pressure vessel design pressures quoted in bar(g) on European-fabricated datasheets and must convert to psig for ASME Section VIII Division 1 compliance verification with US-based owner-engineers.
Hydraulic system designers specifying pumps, valves, and cylinders from German or Italian manufacturers (Rexroth, Parker Hannifin European division, Atos) find all performance curves in bar, requiring conversion for compatibility with US-standard pressure gauges, relief valves calibrated in psi, and NPT-threaded components rated in psig.
In the oil and gas sector, wellhead Christmas tree equipment and pipeline flanges sourced internationally list working pressures in bar — e.g., ANSI Class 600 flanges rated at approximately 99.3 bar at ambient, requiring bidirectional conversion during material requisition and inspection.
Gas cylinder and storage tank labeling in the EU uses bar (200 bar for standard high-pressure cylinders, 300 bar for composite wrapped cylinders), while US DOT cylinders display psi (typically 2,265 psig and 4,500 psig respectively), and the field technician performing a fill station interconnection must confirm the pressure rating compatibility to avoid catastrophic over-pressurization.
HVAC and refrigeration engineers specifying R-410A or CO₂ transcritical systems encounter European condensing unit pressures stated in bar(a) that must be converted to psia for expansion valve selection charts published in US customary units.
Even in laboratory and metrology environments, the bar remains the preferred unit for precision pressure calibrators and deadweight testers in many national metrology institutes, and the cross-check against psi is a routine part of instrument calibration certificate review.
In fire protection engineering, European sprinkler systems designed per EN 12845 list operating pressures in bar, while NFPA 13 systems in the Americas use psi — the conversion is essential during international project reviews and hybrid designs.
Real-World Usage Scenarios
European Hydraulic Power Unit Integration with US Equipment
A US automotive assembly plant receives a German-manufactured hydraulic power unit rated at 280 bar(g) continuous and 350 bar(g) peak. The facility's existing distribution piping is rated for 5,000 psig. Converting: 280 bar(g) × 14.5038 = 4,061 psig, and 350 bar(g) × 14.5038 = 5,076 psig. The peak pressure exceeds the piping rating, requiring either a pressure-limiting valve set to 345 bar(g) = 5,000 psig, or a piping upgrade. Without the precise conversion, the system could have been connected with the false assumption of compatibility.
Gas Cylinder Cross-Border Fill Station Operation
A specialty gas supplier operates fill stations in both Houston (US DOT jurisdiction) and Rotterdam (EU TPED jurisdiction). A customer requests 200-bar nitrogen cylinders. The Houston fill station's manifold is calibrated in psig: the target fill pressure is 200 bar(g) × 14.5038 = 2,901 psig at 70°F. However, DOT 3AA cylinders are rated for 2,265 psig service pressure at 70°F — the 200-bar European fill exceeds the US cylinder rating. The operator must either source 300-bar-capable DOT-spec cylinders or reduce fill pressure to 156 bar(g), illustrating why bar-to-psi conversion is a critical safety step in cross-border cylinder logistics.
Process Vessel Design Code Reconciliation
An international EPC firm is designing a chemical reactor for a site in Singapore, with the vessel fabricated in Italy to EN 13445 and the relief system designed by a US office to ASME Section VIII and API 520. The vessel's design pressure is 25 bar(g) per the European datasheet. The US team converts 25 × 14.5038 = 362.6 psig and specifies a relief valve set at 362.5 psig with a 10% overpressure allowance. However, EN 13445 allows a different overpressure margin than ASME, and the accumulated pressure scenarios differ. Both codes must be reconciled point by point; the unit conversion is only the first step.
Common Mistakes to Avoid
Confusing bar with bar(g)
The notation 'bar' on a European pressure gauge normally means bar(g) — gauge pressure relative to ambient atmosphere — while 'bar(a)' denotes absolute pressure. At sea level, 0 bar(g) = 1.01325 bar(a). US engineers frequently read 'bar' as absolute and convert directly to psia, producing a value roughly 14.5 psi higher than intended when the original was gauge. Always verify from the datasheet context whether the European value is gauge or absolute before converting.
Mixing psi, psia, and psig terminology
The US convention of explicitly labeling psia (absolute) and psig (gauge) does not exist universally. When a European engineer writes '10 bar,' it almost always means 10 bar(g). Converting that to '145 psia' is incorrect — the correct conversion is 145 psig. An error of one atmosphere (14.5 psi) in a 10-bar system represents a 10% error; in a 2-bar low-pressure gas system, it's a 50% error that can cause safety valve mis-setting.
Rounding the conversion factor too aggressively for safety-critical work
Using 14.5 psi/bar instead of 14.5038 for a 350-bar hydraulic system accumulates a 1.33 psi error per bar, totaling roughly 46 psi across the system. For pressure relief valve setpoint verification where the tolerance band may be ±3%, cumulative rounding can push a compliant valve into non-compliance. Always use at least four significant figures for the conversion factor and round only the final reported value.
Ignoring temperature de-rating when converting pressure ratings
A European PN 40 flange is rated for 40 bar(g) at the reference temperature (typically 20°C or 50°C depending on material). At elevated temperatures (200°C+), the allowable pressure drops significantly per EN 1092-1 material tables. Converting 40 bar(g) to 580 psig and comparing against ASME B16.5 Class 300 ratings without adjusting both sides for temperature produces a false equivalence. Always cross-reference the pressure-temperature rating tables, not just the nominal pressure class.
Industry Standards Referenced
Frequently Asked Questions
Is bar an SI unit?
No, bar is not an official SI unit but is widely accepted for use with SI. 1 bar = 100,000 Pa = 0.1 MPa. The official SI unit is the pascal (Pa).
What is the difference between bar and barg?
Bar is absolute pressure, barg is gauge pressure (relative to atmospheric). At sea level, 1 bar = 0 barg. PSI follows the same pattern: psia vs psig.
How do I convert psi to bar?
Divide psi by 14.5038. For quick estimates, divide psi by 14.5. 100 psi ≈ 6.9 bar.
Why do European datasheets use bar instead of MPa?
While MPa is the SI unit, bar gives more intuitive numbers for typical industrial pressures. For example, a 6-bar pneumatic system is easier to read than 0.6 MPa, and a 250-bar hydraulic system avoids decimal fractions. Bar is deeply entrenched in European manufacturing culture and is explicitly permitted under EU pressure equipment directives alongside SI units.
What is the precise conversion factor per NIST?
Per NIST Special Publication 811, the exact conversion is 1 bar = 14.503773773 psi (based on 1 psi = 6,894.757293168 Pa and 1 bar = 100,000 Pa). For engineering calculations, 14.5038 is sufficient; for legal metrology or custody transfer, use the full-precision factor and round only at the final result.
Reviewed for accuracy
Reviewed against ISO 80000-4 and NIST SP 811 standards · Last reviewed: June 7, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.