Frequency Converter

About frequency units

Frequency counts how many times a repeating event occurs per second — the SI unit is the hertz (Hz), meaning exactly one cycle per second. Human hearing spans roughly 20 Hz to 20,000 Hz (20 kHz); audio equipment is specified in this range. Radio broadcasts occupy the kilohertz (AM) and megahertz (FM) bands. Modern CPUs run at gigahertz clock speeds — a 3.6 GHz processor completes 3.6 billion clock cycles every second. Revolutions per minute (rpm) appear in mechanical contexts: an engine spinning at 6,000 rpm runs at exactly 100 Hz. The relationship between frequency and period is simply: period = 1 ÷ frequency, so a 100 Hz signal repeats every 10 milliseconds.

History & origin

The hertz is named after Heinrich Rudolf Hertz, the German physicist who in 1887 was the first to experimentally confirm the existence of electromagnetic waves predicted by Maxwell's equations — demonstrating transmission and reception of radio waves in his laboratory. The unit was officially adopted in his honour by the General Conference on Weights and Measures in 1960, replacing the older designation 'cycles per second' (cps). The megahertz and gigahertz scales became practically important with the rise of commercial radio in the 1920s and semiconductor electronics from the 1950s onward.

Tips

Frequency and period are reciprocals, not proportional — double the frequency and the period halves. This catches out anyone working with oscilloscopes or signal generators: a 1 kHz signal has a period of 1 ms, a 10 kHz signal has a period of 0.1 ms. Also note that rpm and Hz measure the same physical thing (rotational frequency) in different units — engine specs in rpm and electrical motor specs in Hz can describe the same shaft speed and should be compared carefully when coupling machines.

Common questions

What is the difference between Hz and rpm?

Both describe rotational or cyclic frequency. 1 Hz = 1 revolution (or cycle) per second, while 1 rpm = 1 revolution per minute = 1/60 Hz ≈ 0.01667 Hz. A motor running at 3,000 rpm spins at 50 Hz — a useful fact when matching motor speed to AC power-line frequency in industrial applications.

What frequency range can humans hear?

Healthy young adults typically hear from about 20 Hz (a very deep rumble) to 20,000 Hz (20 kHz, a high-pitched hiss). Sensitivity peaks around 1–4 kHz, which is the range of human speech. High-frequency hearing degrades with age — many adults over 50 cannot hear above 12–14 kHz.