Beat Frequency Calculator
Enter two frequencies in hertz to get the beat frequency — the pulsing rate you hear when the waves are superimposed — and see why it fades to nothing as the tones come into tune.
The pulsing rate, instantly
Enter two wave frequencies in hertz and this beat frequency calculator returns the rate of the loudness pulsing as |f₁ − f₂|.
Use the same units
Put both frequencies in hertz so the beat frequency comes back in hertz — one beat per second is 1 Hz of swelling and fading.
What is a beat frequency?
The pulsing of two close tones
A beat frequency is the slow throb you hear when two waves of slightly different frequencies are played together. This beat frequency calculator turns two frequencies in hertz into that pulsing rate, the number musicians listen for when tuning. As the waves drift in and out of step they alternately reinforce and cancel one another, so the combined sound swells and fades. The rate of that swelling — the beats per second — is exactly the difference between the two source frequencies, and it is the cue a piano tuner uses to bring a string into tune by ear.
Enter two frequencies in hertz to get the beat frequency in hertz instantly — the rate at which the combined sound pulses.
The beat frequency is the absolute difference between the two frequencies — the size of the gap between them, regardless of which one is higher.
f_beat = |f₁ − f₂|The vertical bars mean "absolute value", so the order of the two frequencies makes no difference: 440 and 444 give the same 4 Hz beat as 444 and 440. Suppose two tuning forks sound at 440 Hz and 444 Hz. The difference is |440 − 444| = 4, so the combined tone swells and fades 4 times every second — a clear, countable 4 Hz beat. Keep both inputs in hertz and the beat frequency comes back in hertz.
The beat frequency answers a single practical question: how fast does the loudness pulse? A 4 Hz beat, like the two tuning forks above, is heard as a steady, easily counted throbbing four times a second — the very sound a piano tuner listens for. Higher beat frequencies pulse faster and blur into a rough, buzzing quality; very small beat frequencies fade so slowly you can watch a needle on a meter rise and fall. The crucial behaviour is at the bottom of the scale: as the two frequencies approach each other the beat frequency falls toward zero, and when they match exactly the pulsing stops altogether. That silence is the goal of tuning by ear — zero beats means the two tones are identical. This is why bringing a string up to pitch makes the beats slow and then vanish, and why the beat frequency is such a sensitive guide: even a fraction of a hertz of mistuning produces an audible, countable pulse.
The formula is exact, but a couple of practical points are worth keeping in mind.
Close frequencies and audible beats
Beats are only heard clearly when the two frequencies are close — typically within about 15 Hz. When the gap is large the ear stops perceiving a pulsing and instead hears two separate tones or a combination tone, even though the formula still returns their difference. Keep both frequencies in hertz and zero or positive; a negative frequency has no physical meaning, and this calculator covers simple two-wave superposition, not complex multi-tone spectra.