About

Pressure measurement errors propagate through entire engineering systems. A miscalculated seal rating of 2 bar versus 29 PSI can mean the difference between a functioning hydraulic line and a catastrophic blowout. The bar (1 bar = 100 kPa) dominates European and ISO standards, while PSI (pounds per square inch) remains the primary unit in North American industrial, automotive, and HVAC specifications. This converter applies the exact conversion factor f = 14.5037738 PSI/bar derived from the definition 1 bar = 10⁵ Pa and 1 PSI = 6894.757 Pa.

This tool assumes gauge pressure unless otherwise noted. Absolute pressure calculations require adding atmospheric pressure (1.01325 bar or 14.696 PSI at sea level). Results are rounded to 6 decimal places. For cryogenic or ultra-high-pressure applications exceeding 10,000 bar, consult ASME PTC 19.2 calibration standards as material compressibility factors become non-negligible.

Formulas

The conversion between bar and PSI is a linear relationship defined by the ratio of their base SI definitions.

P_PSI = P_bar × 14.5037738

P_bar = P_PSI14.5037738

The factor 14.5037738 derives from the fundamental definitions:

1 bar = 10⁵ Pa = 100,000 Pa

1 PSI = 6,894.757293 Pa

f = 100,0006,894.757293 = 14.5037738

Where P_PSI is pressure in pounds per square inch, P_bar is pressure in bar, and f is the exact conversion factor. One PSI equals one pound-force per square inch, where 1 lbf = 4.4482216 N and 1 in² = 6.4516 × 10⁻⁴ m².

Reference Data

Bar	PSI	kPa	atm	Common Application
0.5	7.252	50	0.494	Low-pressure pneumatics
1	14.504	100	0.987	Atmospheric pressure (approx.)
1.5	21.756	150	1.480	Espresso machine brewing
2	29.008	200	1.974	Bicycle tire (road bike)
2.4	34.809	240	2.369	Standard car tire pressure
3	43.511	300	2.961	Home water boiler
4	58.015	400	3.948	Fire extinguisher
5	72.519	500	4.935	Scuba tank (working pressure)
6	87.023	600	5.921	Industrial compressor output
7	101.526	700	6.908	CO₂ cartridge
8	116.030	800	7.895	Truck tire pressure
10	145.038	1000	9.869	Standard hydraulic systems
12	174.045	1200	11.843	Steam boiler (low-pressure)
15	217.557	1500	14.804	Pressure washer (consumer)
20	290.075	2000	19.738	Nitrogen gas cylinder
30	435.113	3000	29.607	Paintball tank
50	725.189	5000	49.346	Natural gas pipeline
100	1450.377	10000	98.692	High-pressure hydraulics
200	2900.755	20000	197.385	Scuba tank (fill pressure)
300	4351.132	30000	296.077	Hydrogen storage tank
500	7251.887	50000	493.462	Waterjet cutting
700	10152.641	70000	690.846	Hydrogen fuel cell vehicle
1000	14503.774	100000	986.923	Ultra-high-pressure research

Frequently Asked Questions

The exact factor is 14.5037738 PSI/bar, derived from the SI definitions: 1 bar = 10⁵ Pa and 1 PSI = 6,894.757293 Pa. Some simplified references round this to 14.5, which introduces an error of approximately 0.026% - acceptable for tire gauges but problematic for calibrated industrial instrumentation.

The conversion factor itself is a mathematical constant independent of temperature. However, the actual pressure reading on a gauge changes with temperature due to gas laws (Gay-Lussac's Law: P ∝ T at constant volume). For every 10°C increase in tire temperature, expect approximately 0.1 bar (1.45 PSI) rise. Always measure cold pressure for accurate readings.

Gauge pressure (barg, psig) reads zero at atmospheric pressure. Absolute pressure (bara, psia) includes atmospheric pressure on top. The conversion factor 14.5037738 applies identically to both - the difference is the datum point. To convert gauge to absolute: P_abs = P_gauge + 1.01325 bar (or 14.696 PSI at standard sea-level conditions).

Bar is a metric-derived unit adopted by ISO and most European engineering standards (DIN, EN). PSI is rooted in the Imperial system and remains standard in ASME, SAE, and US industrial codes. Most modern pressure transmitters and gauges display both scales. When working across standards, verify whether specifications reference gauge or absolute readings - a 1 atm offset error can cause system failures.

The mathematical conversion is exact at all pressure ranges. However, at pressures exceeding approximately 10,000 bar (145,038 PSI), real-world measurement instruments introduce non-linearities due to elastic deformation of sensing elements. At ultra-high pressures above 50,000 bar, dead-weight testers or diamond anvil cells are used, and conversions should reference NIST traceable calibration data rather than simple multiplication.

Altitude affects atmospheric pressure but not the conversion factor. At 1,500 m elevation, atmospheric pressure drops to approximately 0.845 bar (12.25 PSI). Gauge pressure instruments auto-compensate since they read relative to local atmosphere. Absolute pressure instruments will read lower. For pneumatic systems, reduced ambient pressure means compressors work harder to achieve the same gauge pressure output.