Frequency Converter (Hz, kHz, MHz, GHz, RPM)
Convert a frequency between hertz-based units (Hz, kHz, MHz, GHz) and revolutions per minute (RPM), used for motor and engine speed. Everything runs in your browser.
How the conversion works
Every unit on this page is defined by how many hertz it represents. One hertz is one cycle per second. The input is converted to hertz, then from hertz into the target unit:
result = value × (Hz per source unit) ÷ (Hz per target unit)
RPM counts rotations per minute rather than per second, so 1 Hz = 60 RPM exactly. This single factor of 60 is the only non-decimal relationship on this page.
Frequency and period are reciprocals
Frequency answers "how many times per second", period answers "how long does one cycle take". They are inverses of each other:
period = 1 ÷ frequency and frequency = 1 ÷ period
| Frequency | Period | Context |
|---|---|---|
| 1 Hz | 1 second | A ticking clock |
| 50 Hz | 20 ms | European mains electricity |
| 60 Hz | 16.67 ms | US mains, 60 Hz display refresh |
| 144 Hz | 6.94 ms | Gaming monitor refresh rate |
| 440 Hz | 2.27 ms | Concert pitch A |
| 1 MHz | 1 microsecond | AM radio range |
| 3 GHz | 0.33 nanoseconds | CPU clock cycle |
This relationship explains why a 144 Hz monitor feels smoother than a 60 Hz one: each frame is displayed for 6.94 ms instead of 16.67 ms, so the image updates more than twice as often.
Quick reference table
| From | Hz | kHz | MHz | RPM |
|---|---|---|---|---|
| 1 Hz | 1 | 0.001 | 0.000001 | 60 |
| 1 kHz | 1000 | 1 | 0.001 | 60,000 |
| 1 MHz | 106 | 1000 | 1 | 6 × 107 |
| 1 GHz | 109 | 106 | 1000 | 6 × 1010 |
| 1 RPM | 0.01667 | 0.0000167 | 1.67 × 10-8 | 1 |
Practical examples
Audio and music
Human hearing covers roughly 20 Hz to 20 kHz, though the upper limit declines with age. Concert pitch A is 440 Hz, and each octave doubles the frequency, so the A above is 880 Hz and the A below is 220 Hz. Audio sample rates are given in kHz: CD audio is 44.1 kHz, professional recording often 48 kHz or 96 kHz. The sample rate must be at least twice the highest frequency being recorded, which is why 44.1 kHz suffices for a 20 kHz hearing limit.
Radio and wireless
FM radio occupies 87.5 to 108 MHz, Wi-Fi operates at 2.4 GHz and 5 GHz, and mobile networks span several bands from 700 MHz to 3.8 GHz. Frequency and wavelength are linked by the speed of light: wavelength = 300 ÷ frequency in MHz gives meters. A 100 MHz FM signal has a 3 m wavelength, which is why FM antennas are around 1.5 m (half a wavelength).
Engine and motor speed
Engine speed is quoted in RPM. A car idling at 800 RPM turns at 13.3 Hz, and at 6000 RPM it reaches 100 Hz. AC motor speed relates directly to mains frequency: a two-pole motor on 50 Hz mains runs at 3000 RPM synchronously, and on 60 Hz mains at 3600 RPM. This is why equipment designed for one region runs at a different speed in another.
CPU clock speeds
A 3.5 GHz processor completes 3.5 billion clock cycles per second, each lasting about 0.29 nanoseconds. Clock speed alone does not determine performance, since instructions per cycle, core count, and cache design matter as much or more. Comparing GHz figures is only meaningful within the same processor architecture.
Frequently asked questions
How many RPM is 1 Hz?
Exactly 60 RPM, because one hertz is one rotation per second and a minute contains 60 seconds.
How do I convert RPM to Hz?
Divide by 60. An engine at 3000 RPM runs at 50 Hz.
What is the relationship between frequency and period?
They are reciprocals: period = 1 ÷ frequency. A 50 Hz signal has a period of 0.02 seconds (20 milliseconds).
Why is European mains 50 Hz and US mains 60 Hz?
Historical accident rather than technical necessity. Early generator designs settled on different standards on each continent, and by the time the difference mattered, too much infrastructure existed to change. The practical effect is that synchronous motors run 20% faster on 60 Hz mains.
Does a higher CPU GHz always mean a faster computer?
No. Clock frequency is only one factor. Architecture, instructions per cycle, core count, memory bandwidth, and thermal limits all affect real performance. A 3 GHz modern processor easily outperforms a 4 GHz chip from a decade earlier.
What frequency range can humans hear?
Roughly 20 Hz to 20 kHz for young adults. The upper limit typically drops to around 15 kHz by middle age, which is a normal part of ageing.
Related converters
- Angle converter, for angular velocity in radians per second
- Speed converter, for linear speed at a given rotation rate
- All unit converters