Where does this come from, and can I check it?

The standard was agreed in London in 1939. The figure is taken from Encyclopaedia Britannica, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.

Is this really a music fact?

Yes. It sits on the Music shelf, one of 1,090 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.

What else can I read about it?

The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.

Mondo Knows Facts

Orchestras tune to A at 440 hertz by international agreement

The standard was agreed in London in 1939

An international conference in London in 1939 recommended that the note A above middle C be tuned to 440 hertz. The International Organization for Standardization confirmed the pitch in 1955. Before that, pitch varied between cities and eras, sometimes by a semitone or more.

Tuning fork actuator — Giant Waynesboro Insect · CC BY-SA 4.0 · licence · source

Where this comes from

Encyclopaedia Britannica

Facts that can change over time are reviewed and updated. If something here looks wrong, Mondo would rather know than be confidently incorrect.

Go further

Music trivia Music Sprint

More facts like this

HTTP status code 404 designates a page that cannot be found on a serverThe 400 series indicates client error status codes within the Hypertext Transfer Protocol standard Universal Serial Bus USB standardized computer peripheral connections in 1996A consortium of tech companies created USB to replace mismatched serial and parallel ports ASCII standard established seven-bit character encoding for computers in 1963The American Standard Code for Information Interchange mapped 128 characters to binary numbers Unicode assigns unique digital codes for over 140,000 characters worldwideThe Unicode Consortium created a universal character set supporting every written language National power grids synchronize electrical generator frequency across countriesNorth America operates at sixty hertz while Europe and Asia use fifty hertz AC frequency Standard A4 paper uses a unique mathematical aspect ratioThe side ratio of one to the square root of two preserves proportions when folded

Tags: pitch, tuning, standards

Orchestras tune to A at 440 hertz by international agreement: the short answers

Where does this come from, and can I check it?: The standard was agreed in London in 1939. The figure is taken from Encyclopaedia Britannica, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.
Is this really a music fact?: Yes. It sits on the Music shelf, one of 1,090 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.
What else can I read about it?: The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.