Frequency ↔ Period Converter

The hertz (Hz) — cycles per second — was adopted as an SI unit in 1930 to honor Heinrich Hertz's 1887 experimental confirmation of Maxwell's prediction of electromagnetic waves. Before 1960 or so, the term "cycles per second" (abbreviated cps) dominated engineering; older textbooks and equipment labels from before the changeover still read "cps" where modern equivalents say "Hz." Radio hobbyists still occasionally use the old notation.

The reciprocal relationship T = 1/f is older than Maxwell — Huygens wrote about it in 1669 for pendulums. What changed in the electronic era was the range: pendulum clocks operate at ~1 Hz (1 second periods), AC mains at 50 or 60 Hz (20 or 16.67 ms), audio at 20 Hz - 20 kHz (50 ms - 50 µs), RF broadcast at MHz-GHz (µs-ns), and modern CPU clocks at GHz (100-500 ps). That's 13 orders of magnitude.

Angular frequency ω = 2πf (rad/s) appears in impedance formulas (Xl = ωL, Xc = 1/ωC) because it measures rotational speed in radians rather than cycles. This convention came from mathematical physics where the exponential form e^(jωt) simplifies to vector rotation — still central to every AC circuit analysis today.

Enter either frequency or period; the other updates automatically. The tool accepts SI prefixes on both: kHz/MHz/GHz/THz for frequency; ms/µs/ns/ps for period. Also displays angular frequency ω = 2πf in rad/s and half-period T/2 (the gap between zero crossings of a sine wave).

Common benchmarks: AC line 50 Hz → 20 ms (EU) or 60 Hz → 16.67 ms (US); 32.768 kHz watch crystal → 30.518 µs; 16 MHz Arduino clock → 62.5 ns per instruction cycle; 2.4 GHz WiFi → 417 ps per cycle; 5 GHz CPU → 200 ps. Everything runs client-side; no values leave your browser.