Hz, kHz, MHz, GHz, and RPM Explained

5 min read•June 9, 2026•Reviewed: June 9, 2026

✓Reviewed by Apex Conversion Editorial Team · Last reviewed June 9, 2026

Frequency answers one question: how many times does something repeat per second? The unit is the hertz (Hz) — one cycle per second. The same unit describes a subwoofer reproducing a 40 Hz bass note, a US wall outlet alternating at 60 Hz, an FM station broadcasting at 101.1 MHz, and a processor ticking 4 billion times a second at 4 GHz.

Because those examples span eleven orders of magnitude, frequency is almost never written in plain hertz outside the audio range. Converting between Hz, kHz, MHz, and GHz is a powers-of-ten exercise, and converting RPM — the rotational version used for engines and motors — needs only a factor of 60.

The Prefix Ladder

Each step up the ladder multiplies by 1,000: 1 kHz = 1,000 Hz, 1 MHz = 1,000 kHz (one million Hz), and 1 GHz = 1,000 MHz (one billion Hz). Going down, divide by 1,000. So a 2.4 GHz Wi-Fi signal is 2,400 MHz, 2,400,000 kHz, or 2.4 billion cycles per second.

Each range maps to a different technology domain. Hertz to kilohertz: audio and AC power. Kilohertz to megahertz: AM/FM radio and ultrasound. Megahertz to gigahertz: TV, cellular, Wi-Fi, GPS, and processor clocks. Knowing the domain usually tells you the prefix before you see the number.

Conversion Formulas

kHz = Hz ÷ 1,000
MHz = kHz ÷ 1,000
GHz = MHz ÷ 1,000

RPM and hertz:
Hz  = RPM ÷ 60
RPM = Hz × 60

Example: 3,000 RPM = 50 Hz

RPM: Frequency for Rotating Machines

RPM (revolutions per minute) is frequency measured per minute instead of per second, which suits machinery that rotates a few thousand times a minute. A car engine idling at 750 RPM turns 12.5 times per second (12.5 Hz); at a 6,500 RPM redline it reaches about 108 Hz. Hard drives spin at 5,400 or 7,200 RPM (90 or 120 Hz), and a washing machine's spin cycle runs around 1,200–1,600 RPM.

The 60× factor also explains AC motor speeds. A simple two-pole motor on US 60 Hz power turns at up to 3,600 RPM; on European 50 Hz power, the same motor tops out at 3,000 RPM. That difference is why some appliances behave differently across regions even when the voltage is adapted.

Everyday Frequency Landmarks

Human hearing spans roughly 20 Hz to 20 kHz, narrowing with age from the top. Concert pitch A is 440 Hz, and every octave doubles the frequency. US grid power alternates at 60 Hz, most of the rest of the world at 50 Hz. AM radio sits at 540–1,700 kHz, FM at 88–108 MHz, GPS at 1.57542 GHz, and Wi-Fi at 2.4, 5, and 6 GHz.

Display refresh rates are frequencies too: a 120 Hz phone screen redraws 120 times per second. And modern CPUs boost to 5–6 GHz — at 5 GHz, each clock cycle lasts just 0.2 nanoseconds, in which time light itself travels only about 6 centimeters.

Quick Tips

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Hz → kHz → MHz → GHz: divide by 1,000 at each step.
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RPM to Hz: divide by 60. Hz to RPM: multiply by 60.
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Audio lives in Hz–kHz, radio in kHz–MHz, wireless and processors in MHz–GHz.
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Don't confuse GHz (clock frequency) with Gbps (data rate) — one counts cycles, the other bits transferred.

Frequently Asked Questions

How do I convert RPM to hertz?

Divide RPM by 60, because hertz counts per second and RPM counts per minute. An engine at 3,000 RPM rotates at 50 Hz; an idle speed of 600 RPM is 10 Hz.

Is a higher GHz processor always faster?

Not by itself. Clock speed counts cycles per second, but performance depends on how much work each cycle does, core count, cache, and memory speed. A modern 3 GHz chip easily outruns a decade-old 4 GHz one.

Why does the US use 60 Hz power while Europe uses 50 Hz?

Early electrical pioneers standardized differently — Westinghouse settled on 60 Hz in the US while AEG's 50 Hz spread through Europe. Both work fine; the legacy mainly matters for motor speeds and older clocks that count grid cycles to keep time.

What frequency range can humans hear?

About 20 Hz to 20,000 Hz (20 kHz) for healthy young ears. Sensitivity peaks around 2–5 kHz — the range of human speech — and the upper limit declines naturally with age, often to 12–15 kHz by middle age.

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