AC foundations
Frequency from period
- where
- frequency (Hz)
- period (s)
Explain this equation
Works out frequency from the time taken for one complete cycle. Useful when reading a waveform on a scope.
f is frequency in hertz: cycles per second. T is the period: the time for one full cycle, in seconds.
If one cycle takes T seconds, then 1/T cycles happen in each second. Frequency and period are reciprocals.
Sense check: a 20 ms period is 1 ÷ 0.02 = 50 Hz, the UK mains frequency. Halve the period and the frequency doubles.
Watch out: T must be a full cycle, not a half cycle, and the unit selector must match your reading (ms or s).
Frequency counts complete cycles per second. If each cycle takes T seconds, divide one second by T.
Convert milliseconds to seconds first. A half-cycle is not a whole period.
Enter your values to see the result.
Common mistake
Entering milliseconds directly and losing a factor of 1,000.
Limits
Periodic waveform; T must represent a complete cycle.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.