The **inverse second** or **reciprocal second** (s^{−1}) is a unit of frequency, defined as the multiplicative inverse of the second (a unit of time). It is dimensionally equivalent to:

- hertz (Hz) – the SI unit for frequency
- radian per second (rad⋅s
^{−1}) – the SI unit for angular frequency and angular velocity - becquerel (Bq) – the SI unit for the rate of occurrence of aperiodic or stochastic radionuclide events
- baud (Bd) – the unit for symbol rate over a communication link
- of strain rate.