The size of CDs

The size of CDs or the rule of Twelve

Compact Disc was the name chosen by Philips, because it matched their compact cassette (which everyone ele just called a cassette.)

In a case of serendipity, they eventually chose the magic metric width of 120 millimetres, or 12 cm for CDs (4.7 inches for Americans). As those who burn precious vinyl discs onto CD will know, this makes it very easy to re-scale artwork. Just change 12 inches to 12 centimetres. Was this deliberate? They must have known they would want to reproduce square LP covers on CD reissues. Anyway, it worked.

CD was developed by Philips and Sony, and they made a useful decision to co-operate. The Philips V2000 video cassette system had died in the face of competition from JVC’s VHS format and Sony’s Betamax format. They wanted to avoid the same format war with the new digital format.

In 1979, three years before the 1982 launch of CD, Philips were experimenting with an 11.5 cm disc, while Sony favoured a 10 cm disc. Each were designed to hold 60 minutes of music, longer than any LP record.

Enter Sony president Norio Ohga, a major opera buff. He decided that the new format should be able to hold Beethoven’s 9th Symphony without a break. Or possibly it was Akio Morita, the Sony chairman.

They checked every known recording, and the longest was Furtwangler’s 1951 version, which ran to 74 minutes. There is an alternative tale, that Herbert von Karajan, who was lined up to launch the Philips format (Polygram embraced Philips, Polydor and Deutsche Grammophon), insisted on Beethoven’s 9th as the bench mark.  So it was decreed that 74 minutes should be the length of a CD, and that meant beefing up Philips 11.5 cm to 12 cm. It has also been said that Sony knew that Philips was tooled up for 11.5 cm discs, and the 12 cm switch would delay their headstart.

However, Sony were using U-Matic video tape as the digital master carrier which was limited to 72 minutes. The Furtwangler 1951 recording didn’t emerge on CD until 1997.

So, apparently, the 12 inches to 12 centimetres conversion is accidental. It was only a few years before technology enabled the current 80 minute standard to fit the same disc.


The chosen CD dimension went on to be the standard for computer programs, Video CD, Photo CDs, CD-i, Recordable CDRs, DVDs, recordable DVD-Rs, SACDs, DVD-Audio, Blu-ray and Blu-ray Ultra 24HD discs. Of course by the time you get to Blu-Ray Ultra 24HD there is vastly more storage than on the humble early CD.


CD 12 cm one size

Truly ONE SIZE FITS ALL … CD, DVD, DVD-AUDIO, SACD, DTS-Audio, DVD audio again and 4K Ultra HD Blu-ray. All on 12 cm diameter carriers

Improved technology boosted CD length to 76 minutes, then to 80 minutes. This has inevitably led to self-indulgent albums, padded out with sub-standard material. The discipline of 44 minutes, or 22 minutes a size was simply “right” and still feels so. As new bands in the 2000s insist on vinyl versions, that 44 minute maximum is returning.


See also:

The CD – Perfect Sound Forever
CD Singles