The standard tuning fork.

What is a standard tuning fork?

When musicians, piano tuners or music teachers speak of a standard tuning fork, they mean a fork that sounds the note A at 440 Hz. This is the A in the treble stave, the A above middle C, sometimes written A4. It is the note an orchestra tunes to and the note most electronic tuners use as their default reference.

The fork is marked, usually on the stem, with its note and frequency, for example "A 440". Commercial forks are tuned at the factory, and the pitch is stamped on them.

Another common fork sounds C at 523.3 Hz. That is the C above the A, calculated from A = 440 Hz in equal temperament, the tuning used on modern pianos.

What ISO 16 says

The standard has an official name: ISO 16, "Acoustics: Standard tuning frequency (Standard musical pitch)". It is short and precise. It specifies that the frequency for the note A in the treble stave shall be 440 Hz, and that tuning should be done with instruments that produce this frequency within an accuracy of 0.5 Hz.

ISO 16 was published in 1975 and is still valid. The International Organization for Standardization confirmed it again in 2022. A good standard tuning fork meets this 0.5 Hz tolerance easily: it is one of the reasons the fork has stayed in use for so long.

How A = 440 Hz became the standard

For most of musical history there was no shared pitch. Each city, church and organ had its own A. A tuning fork associated with Handel, dated 1740, sounds A = 422.5 Hz. A fork that belonged to Beethoven, dated around 1800 and now in the British Library, sounds A = 455.4 Hz, more than a semitone higher. Music written for one did not sound the same on the other.

The London conference of May 1939 brought together delegates from France, Germany, the Netherlands, Italy and Britain. Radio and recordings crossed borders, which made a shared pitch more useful than ever. 440 Hz is a convention: nothing in acoustics makes it special.

Do orchestras really tune to 440 Hz?

Many do, but not all. The standard is a reference, not a law. In 1987 the New York Times reported that the A of most symphony and opera orchestras ranged between 440 and 444 Hz. Some orchestras, such as the Berlin Philharmonic, use 443 Hz.

Other pitches are common in specialist fields. Ensembles playing Baroque music on period instruments often use A = 415 Hz, about one equal-tempered semitone below 440 Hz. Some musicians and listeners prefer 432 Hz, about a third of a semitone lower. For playing with others, 440 Hz remains the safe choice.

How to tune with a standard tuning fork

• Hold the fork by its stem and strike one prong on your knee or a rubber pad, never on a hard edge.
• Press the end of the stem onto a wooden surface, or onto the bridge or body of your instrument. The tone becomes much louder.
• Play the matching note: the open A string on a violin or cello, the open fifth string of a guitar, two octaves lower, or the A above middle C on a keyboard.
• Listen for beating, a slow wobble in volume. The slower the beating, the closer you are. When it disappears, the note matches the fork.
• Tune the remaining strings or notes from that A by ear or with a tuner.

A fork gives you one note only. That is its limit and its strength: it needs no battery, it does not drift and it trains your ear. Electronic tuners have largely replaced forks in daily use, but many teachers and piano tuners still carry one.

How accurate is a tuning fork?

Very accurate, provided it is not damaged. The pitch of a steel fork depends on the length and thickness of its prongs and on the stiffness and density of the metal, and none of these change in normal use. Temperature has a small, reversible effect: a typical steel fork changes by about 86 parts per million per degree Celsius. A fork that sounds exactly 440 Hz at room temperature would still be within ISO 16's 0.5 Hz tolerance after a change of about 10 degrees.

What spoils a fork is physical damage. Striking it against metal or stone can dent a prong and change the pitch. Keep it in its case and strike it only on something soft.

Standard pitch and our Fork

The Cosmic Wishing Fork is deliberately not a standard fork. It is tuned to 432 Hz, a slightly lower A, and made to be worn as a ritual object. If you need to tune an instrument for an ensemble, use a 440 Hz fork. If you want a fixed tone to carry with you, join the list to hear when our Fork opens.