Convert a musical note name (like A4) to its frequency in Hz, or the other way — and play the tone to check it by ear.
440 Hz is the most widely used modern concert pitch reference for the note A4, standardized internationally during the 20th century as a common tuning point across orchestras and instrument makers worldwide.
It isn't universal, though — some orchestras and ensembles tune slightly sharp, commonly to 442 or 443 Hz, for reasons ranging from historical tradition to a perceived brighter sound — which is exactly why the reference pitch on this page is editable rather than fixed at 440.
Once your reference pitch is set, every other note's frequency is calculated using equal temperament: each semitone step multiplies or divides the frequency by the 12th root of 2, the mathematical basis of the standard Western tuning system used on virtually all modern fixed-pitch instruments like pianos.
440 Hz is the most common modern concert pitch reference, standardised internationally in the 20th century. It isn't the only one in use — some orchestras tune slightly sharp at 442 or 443 Hz — which is why the reference pitch above is editable.
A tuning system that divides each octave into 12 equal semitone steps, each a frequency ratio of the 12th root of 2 (about 1.0595) apart. It's the standard tuning for pianos and most Western music, though not the only tuning system historically or globally.
A cent is 1/100th of a semitone. If your frequency doesn't land exactly on a note, the result shows how many cents sharp or flat it is from the nearest one — useful for checking how in-tune something is.
