Frequency Calculator — Free Online

Frequency is one of the most fundamental quantities in physics, engineering, and everyday life. It measures how often a repeating event, such as a wave crest, a pendulum swing, or an electrical oscillation, occurs per unit of time. The SI unit of frequency is the hertz (Hz), named after the German physicist Heinrich Hertz, where one hertz equals one cycle per second. Before the adoption of hertz in 1960, frequency was commonly expressed as "cycles per second" (cps). Frequency values span an enormous range: the human heart beats at roughly 1 to 2 Hz, audible sound covers 20 Hz to 20,000 Hz, and visible light oscillates at approximately 400 to 790 terahertz (THz).

The period (T) of an oscillation is the time taken for one complete cycle, and it is the reciprocal of frequency: T = 1/f, and equivalently f = 1/T. This inverse relationship means that higher frequency corresponds to shorter period. For example, the period of 60 Hz alternating current is 1/60 of a second, roughly 16.67 milliseconds. This simple relationship underpins all wave and oscillation analysis and is the basis of the Frequency from Period and Period from Frequency modes in this calculator.

Wavelength (lambda) is the spatial distance over which a wave completes one full cycle, measured from one crest to the next or from any point to the next identical point on the wave. Wavelength, frequency, and wave speed are linked by the universal wave equation: v = f times lambda, which rearranges to lambda = v/f or f = v/lambda. This equation applies to all types of waves, including sound waves in air (speed approximately 343 m/s at 20 degrees Celsius), electromagnetic waves in a vacuum (speed 299,792,458 m/s, usually denoted c), water waves, seismic waves, and waves on a string. Because the wave speed is fixed for a given medium, frequency and wavelength are inversely proportional: doubling the frequency halves the wavelength.

Angular frequency (omega) expresses the rate of oscillation in radians per second rather than cycles per second. Since one complete cycle spans 2 pi radians, the conversion is omega = 2 pi f. Angular frequency appears naturally in the mathematics of circular motion and simple harmonic motion, where displacement is described by x(t) = A cos(omega t + phi). It is also essential in electrical engineering for analysing alternating current circuits, where impedance depends on omega, and in quantum mechanics, where the energy of a photon is E = h-bar times omega (with h-bar = h / 2 pi). Using angular frequency simplifies many equations by eliminating repeated factors of 2 pi.

The electromagnetic spectrum illustrates the vast range of frequencies found in nature. Radio waves have frequencies from about 3 kHz to 300 GHz, microwaves from 300 MHz to 300 GHz, infrared radiation from 300 GHz to 400 THz, visible light from about 400 THz (red) to 790 THz (violet), ultraviolet from 790 THz to 30 PHz, X-rays from 30 PHz to 30 EHz, and gamma rays above 30 EHz. All electromagnetic waves travel at the speed of light in a vacuum, so their wavelength is determined entirely by their frequency.

Frequency has countless practical applications across science and engineering. In music and acoustics, the note A4 is defined as exactly 440 Hz, and each octave represents a doubling of frequency, so A5 is 880 Hz and A3 is 220 Hz. In electrical power systems, the mains frequency is either 50 Hz (used in the UK, Europe, Asia, Africa, and Australia) or 60 Hz (used in North America, parts of South America, and Japan). Computer processors are rated by clock speed in gigahertz, where a 3.5 GHz CPU executes 3.5 billion clock cycles per second. In medicine, ultrasound imaging typically uses frequencies between 2 MHz and 18 MHz, with higher frequencies providing better resolution but less penetration depth. Radio broadcasting uses frequencies from around 530 kHz (AM radio) to over 100 MHz (FM radio), with each station assigned a specific carrier frequency.