A440
A440 is the international standard concert pitch that sets the note A above middle C to a frequency of 440 Hz. Defined by the ISO 16 standard, it serves as the reference from which every other note is calculated. Tuning to A440 lets musicians and instruments play together in tune regardless of where or when they were tuned.
A440 refers to tuning the A above middle C to exactly 440 hertz, meaning 440 vibrations per second. This reference pitch was formalized internationally as the ISO 16 standard, giving orchestras, instrument makers and software a shared anchor. Once A is fixed at 440 Hz, the frequencies of all other notes follow from the equal temperament formula, so agreeing on A alone is enough to keep an ensemble consistent. Some orchestras deliberately tune slightly higher, often to 442 or 443 Hz, to gain a brighter sound, while historical and baroque ensembles may tune lower, around 415 Hz. That is why a good chromatic tuner lets you shift the reference away from 440. On FretMind you can calibrate the reference pitch anywhere from 430 to 450 Hz, matching an ensemble that does not use the default or experimenting with alternative pitch standards while keeping every note correctly related to your chosen A.