Revolutions per minute (abbreviated rpm, RPM, r/min, or r·min−1) is a unit of frequency: the number of full rotations completed in one minute around a fixed axis. It is most commonly used as a measure of rotational speed or angular velocity of some mechanical component.
Standards organizations generally recommend the symbol r/min, which is more consistent with the general use of unit symbols. This is not enforced as an international standard; in French, for example, tr/mn (tours par minute) is commonly used.
The German unit reads 1/min (= 1 min-1); 1 rpm is also 1/min = 1/(60s) = 1/60 Hertz.
