What is a Torr?

The torr equals approximately 1.0000003 mmHg (essentially identical, 133.322 Pa) and is named after Italian physicist Evangelista Torricelli (1608–1647), who invented the mercury barometer. The torr is widely used in vacuum-system specifications, laboratory instruments, and high-vacuum physics. Vacuum levels are categorized: 'low vacuum' is 760 to 1 torr, 'medium vacuum' 1 to 10⁻³ torr, 'high vacuum' below 10⁻³ torr. Mass spectrometers, electron microscopes, and semiconductor manufacturing systems require high vacuum (10⁻⁶ to 10⁻⁹ torr). The torr relates to the mmHg (essentially equal), the pascal (1 torr ≈ 133.3 Pa), the millibar (1 torr ≈ 1.333 mbar), and the atmosphere (760 torr = 1 atm). Modern scientific publications increasingly use the pascal, but the torr remains entrenched in vacuum technology.

Visual reference for how the torr relates to other pressure units. Each row links to the full converter for that pair.

• Vacuum-chamber pressure readings
• Semiconductor manufacturing
• Older physics literature

• ✓1 Torr ≈ 1 mmHg (differ by ~1 ppm — negligible in practice).
• ✓1 atm = 760 Torr exactly.
• ✓Named after Evangelista Torricelli, inventor of the barometer.

• ✗Assuming torr and mmHg are truly identical — they differ by ~10⁻⁷; only matters in metrology.
• ✗Using Torr in everyday context — obscure outside vacuum engineering.
• ✗Mixing Torr and mTorr without specification.