Note Frequency Calculator
Convert a note name and octave into its exact frequency in hertz using equal temperament.
Standard concert pitch sets A4 to 440 Hz. Some orchestras tune a touch higher (442–443 Hz) for brightness, so nudge the reference if you need a different standard.
How it works
Every pitch on a piano maps to a MIDI note number, and A4 — the A above middle C — sits at MIDI 69 with a frequency of 440 Hz by convention. From there the whole scale follows one clean rule.
The formula is f = 440 × 2^((n − 69) / 12), where n is the MIDI number of your note. Because there are twelve equal semitones in an octave, moving up twelve steps doubles the frequency — that's why A5 comes out to 880 Hz, exactly twice A4.
Pick a letter, an accidental, and an octave, and the tool works out the MIDI number and the frequency for you. If your ensemble tunes a little sharp, change the A4 reference and every pitch shifts with it.
Frequently asked questions
Why is A4 exactly 440 Hz?
It's an agreed international standard for concert pitch, set so everyone tunes to the same reference. It's a convention, not a law of physics — some groups use 442 or 432 Hz instead.
What does equal temperament mean?
It splits the octave into twelve identical semitones so music sounds in tune in every key. Each semitone multiplies the frequency by the twelfth root of two, about 1.0595.
Why does going up an octave double the frequency?
An octave is twelve semitones, and twelve steps of multiplying by 2^(1/12) equals multiplying by 2. So A5 is double A4, A6 is double A5, and so on.