How to Convert Bar to Atmospheres (bar to atm)

Updated 5 Oct 2026 in Unit Converters

Pressure conversions are used for tyre pressure (psi or bar), blood pressure readings in mmHg and weather maps in millibars. This guide shows how to convert bar into atmospheres by hand, with examples and a quick-reference table.

The conversion

To convert bar to atmospheres, multiply the value by 0.9869232667. To go the other way, divide by the same number (or multiply by 1.01325). For a quick estimate, multiply by about 0.99.

Atmospheres = bar × 0.9869232667

Worked examples

• 3 bar = 2.9608 atm
• 12.5 bar = 12.3365 atm
• 75 bar = 74.0192 atm

Bar to Atmospheres table

Common questions

Is bar to atm exact?

The factors used here are the internationally defined values where they exist; results are rounded for display only.

How do I convert back?

Use the Atmospheres to Bar converter.

Mistakes to avoid

Multiplying when you should divide

Converting to a smaller unit gives a bigger number, and converting to a larger unit gives a smaller one. If your answer moves the wrong way, you have inverted the factor.

Dropping the units

A bare number without a unit is easy to misread later. Always write the unit with the result.

Rounding the factor too early

Using 3 instead of 3.28 for feet per metre introduces an error of almost 9% before you have started.

Background

Writing the units next to every number while you work is the simplest way to avoid mistakes. If the units do not cancel to leave the one you want, the calculation is set up wrongly.

Unit conversion is simply multiplication by a fixed ratio. The ratio between two units of the same quantity never changes, so once you know it you can convert any value in either direction.

A conversion table is handy for common values, but a calculator is faster and avoids interpolation errors for anything in between.

For any value, use the Bar to Atmospheres Converter or browse all pressure converters.

Run your own numbers: Bar to Atmospheres Converter