Understanding frequency
Cycles per second.
One unit, three orders of magnitude that matter.
The hertz.
A hertz is one cycle per second — one oscillation, one repeat, one tick. Mains electricity in most of the world runs at 50 Hz; in the United States, 60 Hz. Concert pitch (A above middle C) is 440 Hz. The metric prefixes apply, and frequencies of interest tend to climb steeply.
1 GHz ≡ 1 000 000 000 Hz
RPM, BPM, and the everyday cousins.
Engines spin in revolutions per minute, drummers count in beats per minute. Both are frequencies, just expressed per minute instead of per second. The conversion is a single division by sixty.
Practical equivalences
- 1 RPM = 1/60 Hz ≈ 0.01667 Hz
- 60 RPM = 1 Hz
- 1 kHz = 60 000 RPM
- 120 BPM = 2 Hz
Three worked conversions.
2.4 GHz to MHz
1 GHz = 1000 MHz
Multiply by a thousand.
2.4 × 1000 = 2400
= 2400 MHz
3000 RPM to Hz
1 Hz = 60 RPM
Divide by 60.
3000 ÷ 60 = 50
= 50 Hz
50 Hz to kHz
1 kHz = 1000 Hz
Divide by a thousand.
50 ÷ 1000 = 0.05
= 0.05 kHz
A note on the name.
The unit was renamed from "cycles per second" to "hertz" in 1960, in honour of Heinrich Hertz, who first generated and detected radio waves in the 1880s. You may still hear "cycles" on old technical drawings — it's the same thing.
Read next