Torr to Atm Converter

What is a Torr?

The Torr is a unit of pressure named after Evangelista Torricelli, an Italian physicist who invented the barometer in 1643.

It is based on the pressure exerted by a column of mercury. Specifically, 1 Torr is equal to 1 millimeter of mercury (mmHg). Because of this historical connection, scientists and doctors use "Torr" and "mmHg" almost interchangeably, though there is a microscopic difference (less than 0.000015%) that only matters in ultra-precise physics.

What is an Atmosphere (atm)?

The Standard Atmosphere (atm) is a unit based on the average pressure of Earth's air at sea level.

Basically, the air above you has weight. If you are standing at the beach, the column of air pushing down on your head exerts 1 atm of pressure.

Why do we use Mercury?

You might wonder, why define pressure using a toxic liquid metal?

Torricelli originally tried using water. However, water is very light. To measure 1 atm of pressure using water, you would need a glass tube over 10 meters (33 feet) tall!

Mercury is roughly 13.6 times denser than water. This allowed Torricelli to shrink the barometer down to a manageable size (less than 1 meter), making it portable and practical for laboratories.

Common Uses Today

While the Pascal (Pa) is the official SI unit for pressure, Torr and Atm are still standard in specific fields.

1. Medicine (Blood Pressure)

When a doctor measures your blood pressure (e.g., 120/80), those numbers are in mmHg (Torr).

• 120 mmHg = 120 Torr.
• Converted to Atm: 120 / 760 = 0.157 atm.

2. Vacuum Physics

Engineers working with vacuums (removing air from a chamber) use Torr because it handles small numbers well.

• Rough Vacuum: 760 to 1 Torr.
• Medium Vacuum: 1 to 0.001 Torr.
• High Vacuum: < 0.001 Torr.

3. Scuba Diving

Divers use Atmospheres to calculate depth pressure. For every 10 meters you dive, pressure increases by 1 atm.

Conversion Cheat Sheet