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Revolutions per minute (abbreviated rpm, RPM, r/min, or r·min<sup>−1</sup>) is a unit of frequency, commonly used to measure rotational speed, in particular in the case of rotation around a fixed axis. It represents the number of full rotations something makes in one minute. The International System of Units (SI) unit for rotational velocity is the radian per second (rad·s<sup>−1</sup>).