Frequency Calculator
The frequency calculator will let you find a wave's frequency given the wavelength and its velocity or period in no time. You can choose a wave velocity from the preset list, so you don't have to remember, e.g., the speed of sound.
In the text, you'll also find the frequency definition, two frequency formulas (period to frequency and wavelength to frequency), and a few examples showing how to calculate frequency.
If you want to know more about waves, check the wavelength calculator, and if you want to know the frequency of musical notes, check out the note frequency calculator.
Frequency definition and the frequency formula
Have a look at the following model of a wave; it will help you understand the terms used in the frequency definition below it.
Frequency is the number of completed wave cycles per second. In other words, frequency tells us how many wave crests pass a given point in a second.
This frequency definition leads us to the simplest frequency formula:
f = 1 / T
.
f
denotes frequency and T
stands for the time it takes to complete one wave cycle measured in seconds.
The SI frequency unit is Hertz (Hz), which equals 1/s (one cycle per second). Other frequency units include millihertz (mHz), kilohertz (kHz), megahertz (MHz), gigahertz (GHz), and terahertz (THz).
Frequency equation from the wavelength
Have a look at another picture which will allow us to see that frequency is connected to wavelength. Wavelength is the distance between two adjacent crests (or troughs). In other words  it is the length of one wave cycle. The longer the wavelength, the lower the frequency:
Another fact we need  how fast the waves travel at (wave velocity) determines how many of them will pass a given point per second. This means the higher the wave velocity, the higher the frequency.
These two relationships between frequency and wavelength (λ), and between frequency and velocity (v), bring us to the following frequency equation:
f = v / λ
.
How to use the frequency calculator?
Our frequency calculator incorporates the abovementioned frequency formulas, therefore you can use it as a period to frequency calculator or a wavelength to frequency calculator.
How to use it as a period to frequency calculator? (How to find frequency if you know period?)

Input the time in which one wave cycle occurs (period). The calculator will determine the frequency.

You can use this calculator to determine the period, if you know its frequency.
How to use it as a wavelength to frequency calculator? (How to calculate frequency from wavelength?)

Enter the wave velocity into the second field or choose the type of wave and its medium from the list in the first field. By default, it is set to light in a vacuum.

Enter the wavelength, and the frequency value will appear.
So, basically, you can enter any two variables, and the third will appear immediately 😀
Example: How to calculate frequency from the period?
To resolve any doubts about how to calculate frequency from the period, let's analyze some simple examples. Firstly, recall the frequency equation:
f = 1 / T
.
Example 1:
How to find the frequency of a wave in which one cycle is completed in 0.25s:
f = 1 / 0.25 s
f = 4 * 1/s
Remember to convert "1/s" to the frequency unit:
f = 4 Hz
Example 2:
How to find the frequency of a wave in which 360 cycles occur in 1 minute:
f = 360 / 1 min
f = 360 / 60 s
f = 6/s = 6 Hz
Example: How to find the frequency of a wave?
This time, we want to learn how to find the frequency of a wave if you're given the wave velocity and wavelength. You need to use the following frequency formula:
f = v / λ
.
Example 1:
A wave's velocity equals 320 m/s and its wavelength is 8 m. Find its frequency.
f = 320 m/s / 8 m
f = 40/s
f = 40 Hz
Example 2:
Find the frequency of light if wavelength equals 3000 km.
The wave velocity equals the speed of light in vacuum:
v = c ≈ 300,000 km/s
f ≈ 300,000 km/s / 3000 km
f ≈ 100/s ≈ 100 Hz
f ≈ 100 Hz