About

Pressure conversions between bar and atm appear trivial but carry real consequences. In chemical engineering, a 1% pressure misread on a reactor vessel rated at 50 bar translates to roughly 0.5 bar (≈ 7.25 psi) of unaccounted force. That margin can exceed a safety valve's setpoint tolerance. The confusion stems from their near-equivalence: 1 bar = 0.986923 atm. Many practitioners round to 1, accumulating drift across multi-stage calculations. This tool applies the exact SI definition (1 atm = 101325 Pa, 1 bar = 100000 Pa) to eliminate rounding-induced error.

Note: this converter assumes standard mechanical pressure. It does not account for gauge vs. absolute pressure distinctions. If your instrument reads gauge pressure, add local atmospheric pressure before converting. Pro tip: at altitude, local atmospheric pressure drops roughly 1.2% per 100 m of elevation gain.

Formulas

The conversion between bar and atm derives from their definitions in Pascals (Pa), the SI unit of pressure:

1 bar ≡ 100 000 Pa

1 atm ≡ 101 325 Pa

Therefore, bar to atm conversion:

P_atm = P_bar × 100 000101 325

Which simplifies to the exact conversion factor:

P_atm = P_bar × 0.986923267

And the inverse, atm to bar:

P_bar = P_atm × 1.01325

Where P_atm = pressure in standard atmospheres, P_bar = pressure in bar. The ratio 100 000101 325 is an exact rational number derived from SI definitions, not an empirical measurement.

Reference Data

Bar	Atm	Pa	psi	kPa	mmHg (Torr)
0.01	0.009869	1 000	0.14504	1	7.5006
0.1	0.098692	10 000	1.4504	10	75.006
0.25	0.24673	25 000	3.6260	25	187.52
0.5	0.49346	50 000	7.2519	50	375.03
1	0.98692	100 000	14.504	100	750.06
1.01325	1.00000	101 325	14.696	101.325	760.00
2	1.97385	200 000	29.008	200	1 500.1
3	2.96077	300 000	43.511	300	2 250.2
5	4.93462	500 000	72.519	500	3 750.3
10	9.86923	1 000 000	145.04	1 000	7 500.6
14.696	14.504	1 469 600	213.17	1 469.6	11 023
20	19.7385	2 000 000	290.08	2 000	15 001
50	49.3462	5 000 000	725.19	5 000	37 503
100	98.6923	10 000 000	1 450.4	10 000	75 006
200	197.385	20 000 000	2 900.8	20 000	150 013
500	493.462	50 000 000	7 251.9	50 000	375 032
1 000	986.923	100 000 000	14 504	100 000	750 064

Frequently Asked Questions

The bar was defined as exactly 100 000 Pa for metric convenience, while the standard atmosphere was defined as 101 325 Pa based on the average sea-level atmospheric pressure. The 1.325% difference is baked into their SI definitions and cannot be eliminated by rounding.

No. Both bar and atm are defined purely in terms of Pascals, which is a force-per-area unit independent of temperature. The conversion factor 0.986923 is a fixed mathematical ratio. However, the actual pressure reading from your instrument may be temperature-dependent due to thermal expansion of the sensing element.

This converter treats the input as whatever you provide. If you input gauge pressure (barg), the output is also gauge (atm gauge). To convert gauge to absolute, add local atmospheric pressure (approximately 1.01325 bar or 1 atm at sea level) before converting.

A technical atmosphere (at) equals 1 kgf/cm² = 98 066.5 Pa. A standard atmosphere (atm) equals 101 325 Pa. They differ by about 3.3%. This converter uses the standard atmosphere (atm). Confusing the two in HVAC or diving calculations can lead to dangerous errors.

Results are displayed to 10 significant figures internally and rounded for display to 6 decimal places by default. The conversion factor itself (100 000 ÷ 101 325) is an exact rational number, so precision is limited only by floating-point representation (IEEE 754 double, ~15-16 significant digits).

Diving (decompression tables use atm), chemical process engineering (reactor design uses bar or MPa), meteorology (weather maps use hPa = mbar), and autoclave sterilization (medical standards reference atm). Mixing units without converting can cause decompression sickness calculations to err by 1.3% per stage, compounding across multi-stop dive profiles.