Definition:Torr/Also defined as

Torr: Also defined as

The torr can also equivalently be defined as:

The amount of pressure equal to exactly $\dfrac {101 \, 325} {760}$ pascals.

This can be seen to be equivalent to the definition given, as $1$ standard atmosphere is itself defined as exactly $101 \, 325$ pascals.

Older sources may give the definition as $1$ millimetre of mercury, but as the latter is no longer defined in terms of standard atmosphere, and $1$ torr is actually now aproximately equal to $0 \cdotp 99999 \, 98575$ millimetre of mercury.

Sources

• 1969: J.C. Anderson, D.M. Hum, B.G. Neal and J.H. Whitelaw: Data and Formulae for Engineering Students (2nd ed.) ... (previous) ... (next): $2.$ Unit Conversion Factors
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): torr
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): torr