Article — Bar to PSIG Converter
Bar to PSIG conversion: gauge pressure for tires, HVAC, and pneumatics
Bar to PSIG conversion swaps gauge pressure between metric and US units, using the exact 14.5038 factor. A 2 bar tire reads 29.01 PSIG on a US gauge; an HVAC R-410A high-side at 28 bar reads 406 PSIG; a pneumatic line at 7 bar reads 102 PSIG. Both units reference atmospheric pressure as zero, so the atmospheric offset cancels and the conversion is a single multiplication. PSIG (pounds per square inch gauge) specifies the gauge reading explicitly; bar gauge does the same thing under ISO conventions. Pick the field that matches your gauge label, type the value, and the converter handles the rest.
The default 1 bar = 14.504 PSIG covers the road-bicycle range. Quick-pick buttons cover tire pressures (1.8 to 3.0 bar), compressed air systems (5 to 7 bar), and HVAC condenser pressures (10+ bar). Always check the gauge label: PSIG is gauge, PSIA is absolute, and the difference is one atmosphere.
The bar to PSIG formula
PSIG = bar gauge times 14.5038. Bar gauge = PSIG divided by 14.5038. The factor comes from the SI definitions: 1 bar = 100,000 Pa and 1 PSI = 6,894.757 Pa, so the ratio is 100,000 / 6,894.757 = 14.50377. Because both sides of the conversion are gauge pressure (referenced to atmosphere), the atmospheric offset (14.696 PSIA or 1.01325 bar absolute) cancels. The same factor applies to bar absolute to PSIA.
0.5 bar = 7.25 PSIG low pneumatic1 bar = 14.50 PSIG road bicycle2 bar = 29.01 PSIG passenger tire2.4 bar = 34.81 PSIG SUV tire7 bar = 101.53 PSIG pneumatic tool28 bar = 406 PSIG R-410A high sideBar PSIG vs PSIA explained
PSIG (pounds per square inch gauge) is pressure above atmospheric. PSIA (pounds per square inch absolute) is pressure above a perfect vacuum. At sea level, atmospheric pressure is 14.696 PSIA, so PSIA = PSIG + 14.696. A tire reading 32 PSIG holds 46.7 PSIA of total gas pressure. The conversion factor between bar and PSIG (14.5038) is the same as between bar absolute and PSIA, because the atmospheric offset is the same in both units (1 atm = 1.01325 bar = 14.696 PSI).
The "G" in PSIG was added to engineering documents in the 1960s after a series of vessel-rupture incidents where engineers confused gauge and absolute pressure. ASME B40.100 now requires the suffix on every spec, drawing, and instrument label. Bar gauge and bar absolute have no equivalent standard suffixes, which is why ISO documents often spell out the reference instead.
Bar to PSIG for tire pressure
Tire pressure is always gauge. The recommended cold tire pressure is on the door-jamb sticker in PSIG (US) or kPa-gauge / bar-gauge (Europe). A 2.2 bar recommendation converts to 31.91 PSIG, typically rounded to 32 PSIG on a US tire gauge. Compact cars run 2.0 to 2.2 bar (29 to 32 PSIG); sedans 2.2 to 2.4 bar (32 to 35 PSIG); SUVs 2.4 to 2.7 bar (35 to 39 PSIG); pickup trucks 2.5 to 2.8 bar (36 to 41 PSIG). Heavy-duty truck and trailer tires run much higher, 6.2 to 7.6 bar (90 to 110 PSIG).
Bar to PSIG in HVAC refrigerants
HVAC manifold gauges read in PSIG and bar gauge side by side. The high side and low side of a running system tell the technician whether the charge is correct. R-410A, the standard refrigerant in residential AC since 2010, typically runs 28 bar (406 PSIG) high-side and 8 bar (116 PSIG) low-side at 35 degrees C condensing temperature. R-32, the lower-GWP replacement, runs similar values. Legacy R-22 runs lower, around 17 bar (246 PSIG) high-side. R-134a in automotive AC runs 10 bar (145 PSIG) high-side at idle.
HVAC pressure-temperature charts are the conversion bridge for refrigerant charging. Look up the refrigerant, find the saturation pressure at your ambient temperature, then convert bar to PSIG to match your gauge. Most modern manifold gauges show both scales, but only one is the original reading.
Bar to PSIG in pneumatic systems
Shop compressed air runs 6 to 8 bar (87 to 116 PSIG). Most pneumatic tools (impact wrenches, sanders, paint sprayers) are rated for 6.2 bar (90 PSIG) maximum supply. Hoses and fittings carry a maximum working pressure stamped in bar or PSIG. The conversion is identical: 1 bar = 14.5 PSIG, exactly. Larger industrial systems (200 bar / 2900 PSIG) handle high-pressure storage for scuba tanks, paintball, and air-gun applications. The bar to PSIG converter scales linearly across the entire range.
Bar PSIG and temperature
Gas pressure in a sealed container rises with absolute temperature (ideal gas law: PV = nRT). For tires, the rule of thumb is 0.07 bar (1 PSIG) per 5 degrees C of temperature change. Cold winter mornings drop a 2.4 bar (35 PSIG) tire to 2.1 bar (30 PSIG) at minus 10 degrees C. Driving warms tires 10 to 15 degrees C above ambient, raising pressure 0.2 to 0.3 bar (3 to 5 PSIG). Always set tire pressure when the tires are cold and have not been driven more than a couple of miles.
Bar to PSIG at altitude
Gauge pressure depends on the local atmosphere. At sea level, 1 atm = 1.01325 bar absolute = 14.696 PSIA. At 1500 m elevation, atmospheric pressure drops to about 0.84 bar (12.2 PSIA). A sealed tire with 2.4 bar gauge at sea level reads roughly 2.55 bar gauge at altitude because the surrounding atmosphere pushes back less. The bar-to-PSIG factor (14.5038) does not change with elevation, but the gauge reading does. Tire monitoring systems handle the correction automatically; mechanical gauges show the same number anywhere.
Pressure-vessel calculations need PSIA, not PSIG. A 30 PSIG steam line at 250 degrees F holds 44.7 PSIA, and the steam tables are indexed by absolute pressure. Plugging in the gauge reading gives the wrong saturation temperature. Always add 14.696 to convert gauge to absolute before using thermodynamic tables.
Common bar to PSIG mistakes
The first mistake is confusing PSIG and PSIA in engineering specs. ASME B40.100 requires the suffix to avoid this. PSI alone, without G or A, is ambiguous; assume gauge unless the spec says otherwise. The second mistake is reading bar absolute as bar gauge. ISO standards usually mean bar gauge in industrial contexts; meteorology and aviation usually mean bar absolute. The numbers differ by 1.01325, enough to matter in any pressure-vessel design or HVAC charging procedure.