Converting frequency: hertz, kilohertz, megahertz and RPM
A processor is marketed at "2.4 GHz," a tuning fork rings at "440 Hz" (concert pitch A), and a hard drive spins at "7200 RPM." All three numbers describe how often something repeats per second — a frequency — just scaled or expressed differently.
The method
Hertz (Hz) means "cycles per second," and it's the base unit everything else scales from: 1 kilohertz (kHz) = 1,000 Hz, 1 megahertz (MHz) = 1,000,000 Hz, and 1 gigahertz (GHz) = 1,000,000,000 Hz. RPM (revolutions per minute) measures the same kind of thing — repeats per unit time — but per minute instead of per second, so 60 RPM = 1 Hz. To convert RPM to Hz, divide by 60; to go the other way, multiply by 60.
A real example: a 7200 RPM hard drive, in Hz
Divide by 60: 7200 ÷ 60 = 120 Hz. A "7200 RPM" hard drive platter is spinning at 120 revolutions per second — which is also why older drives marketed as "5400 RPM" (5400 ÷ 60 = 90 Hz) feel noticeably slower: the platter is passing data under the read head a third less often per second.
A real example: a 2.4 GHz CPU, in MHz and kHz
Multiply by the conversion factor for each step down: 2.4 × 1,000 = 2,400 MHz, and 2,400 × 1,000 = 2,400,000 kHz. A "2.4 GHz" processor completes 2.4 billion cycles per second, which is why clock speed alone stopped being a useful shorthand for performance once chips hit this range — the number is almost too large to reason about directly, which is exactly why GHz replaced Hz on spec sheets in the first place.
A real example: concert pitch A at 440 Hz, in kHz
Divide by 1,000: 440 ÷ 1,000 = 0.44 kHz. Musical pitch is one of the few places you'll still see a frequency given in plain Hz rather than kHz or MHz, because the numbers involved (roughly 20 Hz to 20,000 Hz, the range of human hearing) are already small and easy to read without scaling.
A real example: a 50 Hz electric motor, in RPM
Multiply by 60: 50 × 60 = 3,000 RPM. This is also why household electricity frequency matters for old-style synchronous motors: a motor built for 50 Hz mains power (standard across most of the world outside the Americas) spins at a different native speed than one built for 60 Hz mains power, independent of anything else about the motor's design.
Why RPM and Hz measure the same thing differently
Both are counting repeats of something over time — RPM just counts over a minute instead of a second, which made sense historically for slower-turning machinery like engines and drives where "revolutions per second" would usually be an awkward fraction. Hz took over for anything fast enough (electrical cycles, radio waves, clock signals) that counting per-minute would produce unwieldy numbers instead.
Run your own numbers
The free Frequency Converter converts between hertz, kilohertz, megahertz, gigahertz and RPM instantly, entirely on your device.