Its SI unit is the reciprocal seconds (s−1); other common units of measurement include the hertz (Hz), cycles per second (cps), and revolutions per minute (rpm).

[1][a][b] Rotational frequency can be obtained dividing angular frequency, ω, by a full turn (2π radians): ν=ω/(2π rad).

It can also be formulated as the instantaneous rate of change of the number of rotations, N, with respect to time, t: n=dN/dt (as per International System of Quantities).

In the special cases of spin (around an axis internal to the body) and revolution (external axis), the rotation speed may be called spin speed and revolution speed, respectively.

Rotational acceleration is the rate of change of rotational velocity; it has dimension of squared reciprocal time and SI units of squared reciprocal seconds (s−2); thus, it is a normalized version of angular acceleration and it is analogous to chirpyness.

An algebraic rearrangement of this equation allows us to solve for rotational frequency:

Rotational frequency can measure, for example, how fast a motor is running.

Rotational speed is sometimes used to mean angular frequency rather than the quantity defined in this article.

where For example, a stepper motor might turn exactly one complete revolution each second.

Rotational frequency is not to be confused with tangential speed, despite some relation between the two concepts.

Imagine a merry-go-round with a constant rate of rotation.

If you stand two meters from the axis of rotation, your tangential speed will be double the amount if you were standing only one meter from the axis of rotation.