Atmospheres to bar (atm to bar) converter

What is an atmospheres to bar converter?

An atmospheres to bar converter is an online tool that translates a pressure value expressed in standard atmospheres (atm) into its equivalent in bar, and vice versa. Both units describe the same physical quantity — pressure, or force applied per unit of area — but they come from slightly different traditions. The standard atmosphere was originally defined to approximate the average air pressure at sea level, while the bar was introduced as a convenient round metric unit. Because the two are very close in magnitude but not identical, a quick converter is useful whenever you need an accurate figure rather than a rough mental estimate.

How it works

The conversion rests on fixed, internationally agreed definitions. One standard atmosphere is defined as exactly 101,325 pascals (Pa), and one bar is defined as exactly 100,000 pascals. Dividing the two definitions gives the conversion factor: 1 atm equals 1.01325 bar. To go the other way, you take the reciprocal, so 1 bar equals about 0.986923 atm.

Because both factors are exact constants, the converter simply multiplies your input by the appropriate number. Enter a value in either field and the other field updates automatically, so you can move from atm to bar or from bar to atm without re-entering anything. The same field also exposes pascals (Pa) and pounds per square inch (psi), making it easy to cross-check against other common pressure units.

Formula

To convert atmospheres to bar, multiply by 1.01325:

$\text{bar} = \text{atm} \times 1.01325$

To convert bar back to atmospheres, multiply by the reciprocal:

$\text{atm} = \text{bar} \times 0.986923$

Atmospheres to bar conversion table

The table below lists common atmosphere values with their bar equivalents (rounded to five decimal places).

Examples

Example 1: Converting 1 atmosphere to bar

A single standard atmosphere is the baseline reference for air pressure at sea level. Multiplying by the conversion factor gives:

$1 \text{ atm} \times 1.01325 = 1.01325 \text{ bar}$

So 1 atm is just over 1 bar — the small difference is exactly why a precise converter matters.

Example 2: Converting 2 atmospheres to bar

Scuba divers often think in terms of “atmospheres absolute.” At roughly 10 metres of seawater the ambient pressure is about 2 atm. Converting:

$2 \text{ atm} \times 1.01325 = 2.0265 \text{ bar}$

Example 3: Converting 1 bar back to atmospheres

Many weather services and tyre gauges report pressure in bar. To express 1 bar in atmospheres:

$1 \text{ bar} \times 0.986923 = 0.986923 \text{ atm}$

This confirms that 1 bar is slightly less than one full atmosphere.

Example 4: Converting 1 atmosphere to pascals

If you switch the target unit to pascals, the converter shows the underlying SI value:

$1 \text{ atm} = 101325 \text{ Pa}$

This is the exact definition from which the bar factor is derived.

Notes

• The standard atmosphere (atm) and the bar are both non-SI units; the SI unit of pressure is the pascal (Pa).
• 1 atm = 101,325 Pa exactly and 1 bar = 100,000 Pa exactly, so the conversion factors carry no rounding error at their source.
• Do not confuse the standard atmosphere with the “technical atmosphere” (at), which is defined differently (1 at = 0.980665 bar).
• For everyday estimates 1 atm ≈ 1 bar is close enough, but engineering, diving, and scientific work usually need the full 1.01325 factor.

Frequently asked questions

How many bar are in 1 atmosphere?

There are exactly 1.01325 bar in one standard atmosphere, because 1 atm is defined as 101,325 Pa and 1 bar is defined as 100,000 Pa.

How do I convert bar to atmospheres?

Multiply the value in bar by 0.986923. For example, 5 bar equals about 4.934615 atm.

Is 1 atm the same as 1 bar?

No, but they are very close. One atmosphere is about 1.3% larger than one bar (1 atm = 1.01325 bar), so they are often treated as roughly equal in casual use but not in precise calculations.

What is the difference between atm and the SI unit pascal?

The pascal is the SI unit of pressure (one newton per square metre). One standard atmosphere equals exactly 101,325 pascals, while one bar equals 100,000 pascals.

Why does the converter also show psi and Pa?

Pressure is reported in many units depending on the field — pascals in science, bar in meteorology and engineering, and psi (pounds per square inch) in the United States. Showing all of them lets you cross-check a single value against whichever unit you need.

Does this converter handle decimals and large numbers?

Yes. You can enter any positive value, including small fractions of an atmosphere or large industrial pressures, and the converted result updates instantly.