Frequency from Period Calculator
Frequency and period are two ways of describing the same repeating signal, and they are tied together by one of the simplest relationships in physics: each is the reciprocal of the other. The period tells you how long a single cycle lasts, measured in seconds, while the frequency tells you how many of those cycles fit into one second, measured in hertz. Flip one and you get the other. A wave whose cycle takes one fiftieth of a second repeats fifty times a second, so its frequency is 50 Hz, and that is exactly the kind of conversion this calculator handles. Enter the period of your signal in seconds and the tool returns the frequency in hertz, along with the same value expressed in kilohertz for higher-frequency signals. This shows up everywhere from mains power and audio tones to clock signals and radio waves. If your period is given in milliseconds, divide by a thousand to convert it to seconds first, since the formula expects seconds. The relationship is exact and works in both directions, so you can read a period off a scope and know the frequency instantly. A worked example below reconciles exactly to the calculator default.
Frequency is the reciprocal of period: f = 1 / T. A period of 0.02 seconds corresponds to a frequency of 50.00 Hz, the cycle repeating fifty times each second.
Frequency formula
f = 1 / T
f = frequency (Hz)
T = period (seconds), time for one cycle
rearranged: T = 1 / f
Frequency counts cycles per second, period measures seconds per cycle, so one is the reciprocal of the other. Dividing one by the period gives the frequency directly.
Worked example
A signal with a period of 0.02 seconds.
- f = 1 / T.
- f = 1 / 0.02.
- f = 50.00 Hz.
These are the calculator's default inputs, so the result above matches the widget exactly.
Frequency from period calculator: frequently asked questions
What is the relationship between frequency and period?
Frequency and period are reciprocals of each other. The period is how long one full cycle takes, in seconds, and the frequency is how many cycles happen each second, in hertz. If a cycle takes half a second, the frequency is two cycles per second, that is 2 Hz. One is simply one divided by the other.
What is a hertz?
A hertz is one cycle per second, the SI unit of frequency. A 50 Hz signal repeats fifty times every second. Kilohertz, megahertz and gigahertz are thousands, millions and billions of hertz, used for audio, radio and processor speeds respectively.
How do I go from frequency back to period?
Take the reciprocal again. The period in seconds equals one divided by the frequency in hertz. A 50 Hz signal has a period of one fiftieth of a second, that is 0.02 seconds or 20 milliseconds. The relationship works both directions.
What if my period is in milliseconds?
Convert it to seconds first by dividing by 1,000, because the formula expects seconds and returns hertz. A period of 20 milliseconds is 0.02 seconds, which gives 50 Hz. This calculator expects the period in seconds.
What is the frequency formula?
Frequency equals one divided by the period, written f equals 1 over T. The period T is in seconds and the frequency f comes out in hertz. For a period of 0.02 seconds, the frequency is 1 divided by 0.02, which is 50 Hz.
Official sources
- The hertz, the second and SI units of time and frequency: US National Institute of Standards and Technology (NIST). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.