Torr to atmospheres (Torr to atm) converter

What is a torr to atmospheres converter?

A torr to atmospheres converter is an online tool that translates a pressure value expressed in torr (Torr) into its equivalent in standard atmospheres (atm), and back again. Both units describe how much force a gas or fluid exerts over an area, but they come from different traditions: the torr grew out of mercury-column barometry, while the standard atmosphere was defined to represent typical pressure at sea level. The converter removes the manual arithmetic so you can move between the two scales instantly and without rounding mistakes.

Torr and standard atmospheres

The torr is named after Evangelista Torricelli, the inventor of the mercury barometer. It is defined so that exactly 760 torr equals one standard atmosphere, which makes one torr almost identical to one millimeter of mercury (mmHg). The torr is widely used in vacuum technology and laboratory work because it conveniently expresses pressures well below normal atmospheric levels.

The standard atmosphere (atm) is a fixed reference unit defined as exactly 101325 pascals. It approximates the average air pressure at sea level and is a familiar baseline in chemistry, meteorology, and engineering. Because both units are tied to the pascal, the relationship between them is exact: 1 torr equals 101325 / 760 ≈ 133.322 pascals.

How it works

To convert from torr to atmospheres, you divide the number of torr by 760, since 760 torr is defined as exactly one atmosphere. To go the other way, you multiply the number of atmospheres by 760. Internally the converter works through the pascal as a common reference: each torr is about 133.322 Pa and each atmosphere is exactly 101325 Pa, so the ratio of those two values is precisely 760.

Formula for conversion

To convert torr to atmospheres:

$\text{atm} = \frac{\text{Torr}}{760}$

To convert atmospheres to torr:

$\text{Torr} = \text{atm} \times 760$

Expressed through the pascal, the same relationships are:

$\text{atm} = \frac{\text{Torr} \times 133.322}{101325}$

Torr to atmospheres conversion table

The table below lists common torr values and their equivalents in standard atmospheres.

Examples of conversion

Example 1: One standard atmosphere

A barometer reads 760 torr at sea level. Dividing by 760 gives exactly 1 atmosphere:

$\frac{760}{760} = 1 \text{ atm}$

This is the defining relationship between the two units.

Example 2: Atmospheres back to torr

A gas cylinder is regulated to 1 atm. Multiplying by 760 returns the value in torr:

$1 \times 760 = 760 \text{ Torr}$

Example 3: Two atmospheres

A pressurized vessel holds 2 atm. Converting to torr:

$2 \times 760 = 1520 \text{ Torr}$

Example 4: A larger reading

An industrial reading of 7600 torr converts to ten atmospheres:

$\frac{7600}{760} = 10 \text{ atm}$

Notes

• The relationship 1 atm = 760 torr is exact by definition, so conversions between the two units involve no measurement error.
• One torr is nearly identical to one millimeter of mercury (mmHg); the two differ only in the seventh significant figure, so for everyday work they are interchangeable.
• The torr is most useful in the vacuum range (pressures far below 760 torr), while atmospheres are convenient for pressures near or above sea-level conditions.
• The converter also supports related units such as pascals, bars, and psi, so you can cross-check a value in several scales at once.

Frequently asked questions

How many torr are in one atmosphere?

There are exactly 760 torr in one standard atmosphere. This is the definition of the torr, so the conversion is precise rather than approximate.

How do I convert torr to atmospheres?

Divide the number of torr by 760. For example, 380 torr divided by 760 equals 0.5 atm. To reverse the calculation, multiply atmospheres by 760.

Is a torr the same as a millimeter of mercury?

They are almost the same. One torr equals exactly 1/760 of an atmosphere, while one mmHg is defined from the density of mercury and standard gravity. The difference is less than one part in a million, so in practice torr and mmHg can be treated as equal.

What is the pressure value of one torr in pascals?

One torr equals 101325 / 760, which is approximately 133.322 pascals. Multiplying any torr value by 133.322 gives the pressure in pascals.

Why is the torr used in vacuum technology?

The torr conveniently expresses very low pressures. A vacuum reading of a few torr, or even a fraction of a torr, is easy to write and compare, whereas the same value in atmospheres would be a small decimal. If you need to work with pascals instead, you can use our pascal to atmosphere converter.

How many atmospheres is 760 torr?

Exactly 1 atmosphere. Because 760 torr is the definition of one standard atmosphere, dividing 760 by 760 always yields a value of 1 atm.