Unit Converters guide
Hertz to RPM, MHz and GHz: Frequency Explained Simply
ยท 4 min read
Frequency is how many times something repeats per second, and 1 hertz (Hz) means once per second. The metric prefixes work as usual: 1 kHz = 1,000 Hz, 1 MHz = 1,000,000 Hz, 1 GHz = 1,000,000,000 Hz. Rotating machines use revolutions per minute (rpm), and because a minute has 60 seconds, 60 rpm = 1 Hz. A hard drive spinning at 7,200 rpm turns 120 times a second.
Below is what those numbers mean in the devices around you, plus a couple of related calculations a unit converter alone won't do.
The units at a glance
| Unit | Cycles per second | Typical use |
|---|---|---|
| rpm | 1/60 | Engines, motors, drives, turntables |
| Hz | 1 | Mains power, audio, display refresh |
| kHz | 1,000 | Audio, AM radio |
| MHz | 1,000,000 | FM radio, older processors |
| GHz | 1,000,000,000 | Wi-Fi, mobile networks, modern CPUs |
Rotation: rpm and Hz
To convert rpm to Hz, divide by 60. To go from Hz to rpm, multiply by 60.
- A 7,200 rpm hard drive: 120 Hz. A 5,400 rpm laptop drive: 90 Hz.
- An engine idling at 1,000 rpm: about 16.67 Hz. At 3,000 rpm: 50 Hz.
- A vinyl LP at 33โ rpm: about 0.556 Hz, just over half a turn per second.
Mains electricity runs at 50 Hz in most of the world and 60 Hz in North America and some other countries. That is 3,000 and 3,600 cycles per minute, which is why simple two-pole synchronous motors connected to the grid spin at exactly those speeds.
Sound and audio
Musical pitch is frequency. The note A above middle C is tuned to 440 Hz, or 0.44 kHz. Human hearing spans roughly 20 Hz to 20 kHz, and the upper limit drops with age.
Radio, Wi-Fi and processors
- AM radio: a station at 1,440 kHz is at 1.44 MHz.
- FM radio: 98.5 MHz is 98,500 kHz.
- Wi-Fi: the 2.4 GHz band is 2,400 MHz; there are also 5 GHz and 6 GHz bands.
- CPUs: a processor running at 3.5 GHz is at 3,500 MHz: 3.5 billion clock cycles per second.
Clock speed alone doesn't decide how fast a processor is, because different chips do different amounts of work per cycle.
Displays and refresh rates
Monitor refresh rates are frequencies too. A 144 Hz display redraws the image 144 times per second (0.144 kHz). That leads to the most useful related calculation: the period.
Beyond conversion: period and wavelength
Two calculations come up constantly alongside frequency.
Period = 1 รท frequency. It tells you how long one cycle lasts.
- 50 Hz mains: 1 รท 50 = 20 ms per cycle.
- 144 Hz monitor: 1 รท 144 โ 6.94 ms per frame.
Wavelength = speed รท frequency. For radio waves, the speed is the speed of light, 299,792,458 m/s.
- 2.4 GHz Wi-Fi: 299,792,458 รท 2,400,000,000 โ 12.5 cm.
- 98.5 MHz FM: โ 3.04 m, which is why FM antennas are much longer than Wi-Fi ones.
The converter changes frequency units; for the time side of these calculations, the Time Converter turns seconds into milliseconds and back.
How to use the Frequency Converter
The Frequency Converter has five units:
- Enter a value in Value.
- Choose From and To: hertz, kilohertz, megahertz, gigahertz or revolutions per minute. The โ button swaps them.
- Read the result, or the table, which shows the same frequency in all five units at once.
Results show up to 10 significant digits; very large values switch to scientific notation. The copy button gives a plain number without thousands separators, ready to paste into a spreadsheet or code.
Common mix-ups
- MHz vs MB/s. A frequency in megahertz is not a data rate. For storage and bandwidth, use the Data Storage Converter.
- rpm vs angular speed. Physics problems often use radians per second; 1 rpm = 2ฯ รท 60 โ 0.1047 rad/s. For converting the angle part, see the Angle Converter.
- Hz on a TV box. Some TVs advertise "motion rate" figures that are higher than the panel's true refresh rate. Check the native refresh rate in the spec sheet.
FAQ
How many Hz is 1 GHz?
1,000,000,000 Hz, one billion cycles per second.
Is rpm a frequency?
Yes. It counts full rotations per minute, so it is a frequency with minutes instead of seconds as the time base.
Why do some countries use 50 Hz and others 60 Hz?
Different early electrical companies chose different standards, and the choices stuck as national grids were built. Both work fine; appliances are designed for one or the other, or both.
Convert hertz, kilohertz, megahertz, gigahertz and rpm with the Frequency Converter.