How many atm is 1 bar?

1 bar is equal to 0.986923 standard atmospheres (atm). This comes from the definition of one standard atmosphere as exactly 101,325 pascals and one bar as exactly 100,000 pascals. Dividing 100,000 by 101,325 gives 0.986923 atm per bar. Bar and atm are close in value but not the same: bar is a metric unit while atm is based on the average atmospheric pressure at sea level.

What is the difference between bar and atm?

Both bar and atm are units of pressure, but they are defined differently. One standard atmosphere (1 atm) is defined as exactly 101,325 pascals, which is the approximate average air pressure at sea level. One bar is defined as exactly 100,000 pascals, a round number close to but slightly less than 1 atm. In practical terms they are nearly equal (within about 1.3%), but scientifically they are distinct. Bar is preferred in meteorology, oceanography, and engineering, while atm is common in chemistry and physics, particularly when describing gas behaviour.

How do I convert atm back to bar?

To convert from atm to bar, multiply the atm value by 1.01325. This is because 1 atm equals 101,325 pascals and 1 bar equals 100,000 pascals, so 1 atm = 101,325 / 100,000 = 1.01325 bar. For example, 2 atm = 2 x 1.01325 = 2.0265 bar. This calculator supports both directions: enter a bar value to get atm, or an atm value to get bar.

Bar to ATM Conversion Calculator

This calculator converts pressure values between bar and standard atmospheres (atm), the two units you meet most often on tyre gauges, weather charts, scuba dive tables and chemistry problem sheets. Bar and atm look almost interchangeable, but they are defined differently: one atm is exactly 101,325 pascals, the average air pressure at sea level, while one bar is a round 100,000 pascals, so the two differ by about 1.3%. Enter a figure into either the bar field or the atm field and the tool works out the other automatically, using the exact factor 1 bar = 0.986923 atm, or the reverse, 1 atm = 1.01325 bar. Alongside the headline result you get the same pressure expressed in kilopascals and psi, a full conversion breakdown showing the value in pascals, kPa and psi, and a plain-language verdict summarising both figures. A reference table further down lists common conversions from 0.01 bar up to 1000 bar, spanning vacuum systems to deep-sea pressure, and a worked example walks through the formula step by step. Use it to translate a tyre pressure spec, a boiler or hydraulic rating, a dive depth, or a chemistry gas-law problem into the unit you need, without rounding errors creeping in. Because the conversion factor is an exact SI relationship rather than an estimate, results stay accurate to six significant figures for any input you enter.

Calculate.co.nz is proud to be partnered with Health Based Building, a leader in sustainable and health-conscious building innovation. With over a century of experience, they develop high-performance systems like Foreverbreathe Specification, Magnum Board, and Foreverbreathe Paints to support energy-efficient, non-toxic living environments. Their commitment to healthier homes aligns with our belief that informed choices lead to better outcomes for Kiwi households.

Calculate.co.nz partner: Health Based Building

Updated Based on SI definitions: 1 atm = 101,325 Pa; 1 bar = 100,000 Pa.

1. Bar to ATM

Pressure in bar

bar

Result in atm

atm

2. ATM to Bar

Pressure in atm

atm

Result in bar

bar

Conversion Result

Input (bar)

bar

Result (atm)
0.986923
standard atmospheres

Also in kPa

100

kilopascals

Bar to ATM Reference Table

Bar	ATM	kPa	psi

Conversion Details

Input value1 bar

Conversion factor1 bar = 0.986923 atm

Result in atm0.986923 atm

Result in Pa100,000 Pa

Result in kPa100 kPa

Result in psi14.503774 psi

Worked Example

Formulaatm = bar x (100,000 / 101,325)

Simplifiedatm = bar x 0.986923

Example: 1 bar1 x 0.986923 = 0.9869 atm

Example: 5 bar5 x 0.986923 = 4.9346 atm

Example: 10 bar10 x 0.986923 = 9.8692 atm

Reverse: atm to barbar = atm x 1.01325

Result: 1 bar equals 0.986923 atm (standard atmospheres). Bar is approximately 1.3% less than one atmosphere.

How to Convert Bar to ATM

The conversion from bar to standard atmospheres (atm) uses the exact SI definitions of both units. One standard atmosphere is defined as exactly 101,325 pascals (Pa). One bar is defined as exactly 100,000 Pa. To convert bar to atm, divide by 101,325 and multiply by 100,000, which simplifies to multiplying by the factor 0.986923266...

Formula: atm = bar x (100,000 / 101,325) = bar x 0.986923

To go the other way (atm to bar), multiply by 1.01325: bar = atm x 1.01325.

Bar vs ATM: Key Differences

Property	Bar	ATM (Standard Atmosphere)
Definition	Exactly 100,000 Pa	Exactly 101,325 Pa
Origin	Metric, practical round number	Average sea-level air pressure
1 unit in psi	14.5038 psi	14.6959 psi
Relation	1 bar = 0.986923 atm	1 atm = 1.01325 bar
Common use	Meteorology, engineering, tyre pressure	Chemistry, physics, gas laws

When Each Unit Is Used

Bar is widely used in engineering and industry across Europe and in meteorology worldwide. Weather charts commonly report pressure in millibars (mbar), where 1 mbar = 0.001 bar. Tyre pressure gauges in many countries use bar. Industrial equipment ratings such as boiler pressure, hydraulic systems, and gas cylinders are frequently stated in bar.

The standard atmosphere (atm) is common in chemistry and physics, particularly when working with gas laws such as Boyle's Law and the ideal gas law. Standard temperature and pressure (STP) is defined as 0 degrees Celsius and 1 atm. Many textbook problems and chemistry calculations use atm as the unit of pressure.

Common Bar to ATM Conversions

Bar	ATM	Practical context
0.5 bar	0.4935 atm	Below-ambient (vacuum system)
1 bar	0.9869 atm	Approximately sea-level air pressure
1.01325 bar	1.0000 atm	Exactly 1 standard atmosphere
2 bar	1.9738 atm	Typical car tyre gauge pressure (above ambient)
3 bar	2.9608 atm	Mountain bike / gravel tyre pressure
10 bar	9.8692 atm	Scuba diving at 90 m depth
100 bar	98.6923 atm	High-pressure industrial systems
1000 bar	986.923 atm	Deep-sea pressure (approx 10 km)

Related Calculators

Essential Calculators: full collection of converters and tools.
Bar to PSI Conversion: convert bar to pounds per square inch.
kPa to PSI Conversion: convert kilopascals to psi.
ATM Conversion: convert atmospheres to other pressure units.
ATM to Pascals Conversion: convert atm to pascals.

Sources and method: International Bureau of Weights and Measures (BIPM) SI Brochure: 1 standard atmosphere = 101,325 Pa (exact); 1 bar = 100,000 Pa (exact). Conversion factor: 100,000 / 101,325 = 0.98692326671... National Institute of Standards and Technology (NIST) Handbook 44.

This converter uses the exact SI definition of both units. Results are rounded to six significant figures for display. For scientific work, use the full factor: 1 bar = 0.98692326671601 atm.