Hertz to RPM Converter

Hertz counts cycles per second and rpm counts revolutions per minute, so if one cycle is one full turn, rpm = Hz × 60. 1 Hz is 60 rpm, 25 Hz is 1500 rpm and 120 Hz is 7200 rpm. That fits anything where you measure the rotation itself: a strobe or optical tachometer reading, a spin rate from video, or a vibration peak at the running speed of a shaft.

The ×60 rule assumes one cycle per revolution, which is not true for an AC motor on a mains supply or a variable-frequency drive. The magnetic field of a motor turns at its synchronous speed, rpm = 120 × Hz ÷ poles:

Only a 2-pole motor matches the plain ×60 conversion. Induction motors also run a little below synchronous speed under load, so a 4-pole motor on 50 Hz might have a nameplate speed such as 1450 rpm. That shaft turns at 24.1667 revolutions per second, which is what a vibration analyser would show as its running-speed peak.

A tachometer or fan sensor often gives more than one pulse per revolution. If the signal you are measuring has several pulses per turn, divide the frequency by that number before converting, or the rpm will be a multiple of the true speed. The converter has no way to know how many pulses your sensor gives per turn.

For disk drives, the familiar ratings convert the other way: 7200 rpm is 120 Hz and 5400 rpm is 90 Hz.

Physics and control formulas often want angular speed in rad/s, which is not in this menu. Multiply hertz by 2π: 50 Hz is 314.16 rad/s, which is also 3000 rpm. From rpm, multiply by 2π and divide by 60.