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Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is the number of turns in one minute. It is a unit of rotational speed or the frequency of rotation around a fixed axis.

International System of Units

According to the International System of Units (SI), rpm is not a unit. This is because the word ''revolution'' is a semantic annotation rather than a unit. The annotation is instead done as a subscript of the formula sign if needed. Because of the measured physical quantity, the formula sign has to be for (rotational) frequency and or for angular velocity. The corresponding basic SI derived unit is s−1 or Hz. When measuring angular speed, the unit radians per second is used. :$\begin 1~&\text &&=& \frac~&\text &&=& \frac~&\text \\pt2\pi~&\text &&=& 1~&\text &&=& 60~&\text \\pt\frac~&\text &&=& \frac~&\text &&=& 1~&\text \end$ Although they have the same dimensions (s−1), hertz (Hz) and radian per second (rad/s) are two different units, representing two different but proportional ISQ quantities: frequency and angular frequency (angular speed, magnitude of angular velocity). The conversions between a frequency (measured in hertz) and an angular velocity (measured in radians per second) are: :$\omega = 2 \pi f\,, \qquad f = \frac \,.$ Thus a disc rotating at 60 rpm is said to be rotating at either 2 rad/s or 1 Hz, where the former measures the angular velocity and the latter reflects the number of revolutions per second. If the non-SI unit rpm is considered a unit of frequency, then . If it instead is considered a unit of angular velocity and the word "revolution" is considered to mean 2 radians, then .

Examples