What is atmosphere?
An atmosphere (atm) is a pressure unit equal to mean atmospheric pressure at sea level, approximately 101,325 pascals. It is used as a reference in chemistry, diving tables, and altitude calculations.
Real-world uses
Atmospheres are used as a reference pressure in chemistry (standard conditions: 1 atm, 25°C), scuba diving (each 10 m of seawater adds about 1 atm), and high-pressure industrial applications like autoclaves and pressure vessels.
History
The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at 0°C under standard gravity. Evangelista Torricelli first measured atmospheric pressure in 1644 using a mercury barometer, establishing this foundational concept.
Common mistakes
Confusing standard atmosphere (101,325 Pa) with technical atmosphere (1 kgf/cm² ≈ 98,066.5 Pa). Also, assuming atmospheric pressure is constant at 1 atm everywhere—it varies with altitude, weather, and temperature.
What is torr?
A torr is a pressure unit equal to approximately 1/760 of an atmosphere. It is used in vacuum technology, low-pressure experimental physics, and blood pressure measurement in older clinical literature.
Real-world uses
Torr is used in vacuum technology, semiconductor manufacturing, and blood pressure measurement (mmHg ≈ torr). Vacuum chambers for electron beam welding operate at about 10⁻⁵ torr, and freeze-drying processes typically operate at 0.1–1 torr.
History
Named after Evangelista Torricelli, who invented the mercury barometer in 1644. The torr was defined to approximate the pressure exerted by 1 mm of mercury. It was formally standardized as 1/760 of a standard atmosphere.
Common mistakes
Assuming torr and mmHg are exactly the same—they are nearly identical but differ by about 0.000015%. For most purposes they are interchangeable, but ultra-precise vacuum work may require distinction.
When is this conversion used?
Converting between atmosphere and torr is common when working across metric and imperial systems, such as international trade, travel between countries with different measurement standards, or following instructions from a different region. Tyre pressure gauges, HVAC systems, and industrial equipment may use different pressure units depending on the manufacturer and region. Converting between psi, bar, and kPa is common in automotive and engineering work.
Worked examples
1 atmosphere = 760 torr
1 torr = 133.32236842 pascal
How to convert atmosphere to torr
To convert atmosphere to torr, multiply the value by 760.
To convert torr back to atmosphere, multiply by 0.00131579.
Measurement standards
The pascal (Pa) is the SI derived unit of pressure, defined as one newton per square metre. The World Meteorological Organization mandates the hectopascal (hPa) for atmospheric pressure reporting in aviation and weather services.
Did you know?
The pressure at the bottom of the Mariana Trench, nearly 11 km deep, exceeds 1,086 bar — over a thousand times atmospheric pressure. At this depth, water is compressed by about 5%, making it measurably denser than at the surface.
Quick reference: atmosphere to torr
| atmosphere | torr |
|---|---|
| 0.1 | 76 |
| 0.5 | 380 |
| 1 | 760 |
| 2 | 1,520 |
| 5 | 3,800 |
| 10 | 7,600 |
| 25 | 18,999.99999999 |
| 50 | 37,999.99999999 |
| 100 | 75,999.99999997 |
| 250 | 189,999.99999993 |
| 500 | 379,999.99999986 |
| 1,000 | 759,999.99999973 |
Common values
| atmosphere | torr | |
|---|---|---|
| Car tyre | 2.17123119 atmosphere | 1,650.13570195 torr |
| Standard atmosphere | 1 atmosphere | 760 torr |
| Blood pressure (systolic) | 0.15790772 atmosphere | 120.00986923 torr |
| Deep-sea submersible | 1,085.61559339 atmosphere | 825,067.85097429 torr |
| Bicycle tyre | 6.11892425 atmosphere | 4,650.38243276 torr |