Frequency Converter (Hz, kHz, MHz, RPM)
Convert frequency between hertz, kilohertz, megahertz, gigahertz, revolutions per minute, and beats per minute.
Frequency conversion reference
| 1 unit | Hz | kHz | MHz | RPM |
|---|---|---|---|---|
| 1 Hz | 1 | 0.001 | 0.000001 | 60 |
| 1 kHz | 1 000 | 1 | 0.001 | 60 000 |
| 1 MHz | 1 000 000 | 1 000 | 1 | 60 000 000 |
| 1 GHz | 1 000 000 000 | 1 000 000 | 1 000 | 60 000 000 000 |
| 1 RPM | 0.0166667 | 0.0000166667 | 0.0000000166667 | 1 |
| 1 BPM | 0.0166667 | 0.0000166667 | 0.0000000166667 | 1 |
Converting frequency units
Frequency counts how many times something repeats per second. The SI unit is the hertz (one cycle per second), and the kilo/mega/giga prefixes step it up by factors of a thousand. Rotational and rhythmic rates are usually quoted per minute instead, which is where RPM and BPM come in.
Per second vs per minute
RPM (revolutions per minute) and BPM (beats per minute) are both counts per minute, so converting to hertz means dividing by 60: 60 RPM is exactly 1 Hz, and a 120 BPM tempo is 2 Hz. Going the other way, multiply hertz by 60. This is the conversion people most often need and most often get upside down.
Where the big units show up
Audio lives in the tens of hertz to about 20 kHz; microcontroller clocks run at megahertz; Wi-Fi and mobile radios work in gigahertz. A 2.4 GHz radio is 2 400 000 000 cycles per second — which is also why its wavelength is only a few centimetres.
Worked example
An engine at 3000 RPM turns 3000 / 60 = 50 times per second, or 50 Hz. A 16 MHz microcontroller clock ticks 16 million times a second. To find the matching wavelength of a radio frequency, use thewavelength calculator; for the period (time per cycle), take 1 / frequency — a 50 Hz cycle lasts 20 ms.
Common questions
- How do I convert RPM to hertz?
- Divide by 60. RPM counts revolutions per minute and hertz counts cycles per second, so 3,000 RPM is 50 Hz and 1,800 RPM is 30 Hz. Going the other way, multiply hertz by 60. It is worth knowing that a 50 Hz mains motor with two poles runs near 3,000 RPM for exactly this reason.
- What is one hertz?
- One cycle per second. The unit is named after Heinrich Hertz and replaced the older "cycles per second", which meant the same thing. A 1 Hz signal repeats once a second; middle A on a piano is 440 Hz; FM radio sits around 100 MHz, or a hundred million cycles a second.
- Is a kilohertz exactly 1,000 hertz?
- Yes. Frequency uses SI prefixes strictly, so kHz, MHz and GHz are always factors of a thousand — there is no binary ambiguity here of the sort that affects data sizes. 1 GHz is exactly 1,000,000,000 Hz.
- What is the difference between hertz and radians per second?
- They measure the same thing on different scales. Hertz counts complete cycles; radians per second measures angular progress round a circle, and one full cycle is 2π radians. So ω = 2πf, and a 50 Hz signal is about 314 rad/s. Circuit analysis usually works in rad/s because the maths of sines and phasors comes out cleaner, while specifications are quoted in hertz because that is what people measure.