440 Hz tone — the A440 concert-pitch reference
A steady 440 Hz sine tone, ready to play. This is A440 — the internationally standardized reference pitch for the A above middle C, and the note most instruments and orchestras tune against. Press Play below; the frequency, waveform and volume are all still adjustable if you want to compare against a sharper or flatter tuning.
What A440 is, and why this exact number
440 Hz is the frequency assigned to the note A above middle C — written A4 in scientific pitch notation, or MIDI note 69 — under the standard 12-tone equal-tempered tuning system used throughout Western music. Every other note's frequency in that system is derived from this one reference by multiplying or dividing by powers of the twelfth root of two, so choosing A440 effectively fixes the pitch of every note on the scale at once.
The number itself is a standardization, not a law of physics. Concert pitch drifted for centuries before instrument makers, orchestras and standards bodies converged on 440 Hz as a common reference in the 20th century, and it remains the most widely used value today — though, as the FAQ below covers, "widely used" is not the same as "universal."
How to use this to tune something
- Press Play above and let the tone ring out on its own for a moment so your ear settles on the pitch.
- Play the same note — an A in the same octave — on your instrument, either alongside the tone or alternating quickly between the two.
- Listen for a slow wavering or "beating" sound where the two pitches are close but not identical; the beating slows down and disappears as you tune closer to a match.
- Adjust your instrument, not the tone, until the beating stops and the two notes lock together.
Want a different reference pitch — 442 Hz, 415 Hz, or any other frequency — instead? Use the frequency slider and number field on the main tone generator, which this page shares.
Frequently asked questions
Is 440 Hz exactly the note A?
Yes — 440 Hz is defined as A4, the A above middle C, in the standard 12-tone equal-tempered scale used throughout Western music. It is the reference every other note on that scale is calculated from.
Do all orchestras really tune to 440 Hz?
No. 440 Hz is the widely used international reference, but plenty of orchestras tune slightly sharp of it — 442 or 443 Hz is common in parts of Europe — for a brighter ensemble sound, and it is a conductor's or orchestra's choice rather than a fixed rule. Historically-informed early-music ensembles often tune well below it, commonly around 415 Hz.
What instrument note should I match against this tone?
Any instrument's A in the same octave as the treble-clef A above middle C — an open A string on a violin, the A key on a piano near the centre of the keyboard, or an A fingered on a wind instrument. Play the tone and the instrument's note together (or alternate quickly between them) and listen for a slow beating or wavering, which fades out as the two get closer in pitch.