Why Records Spin at 33⅓
Lift the lid on a record player and look at the speed switch. There's 45, which is at least a whole number. And there's 33⅓.
Thirty-three and a third revolutions per minute. Not 30. Not 35. A third of a turn more than 33, every minute, on almost every turntable in the world.
It looks like the kind of number nobody would choose on purpose. And in a way, nobody did. At least, not for music.
The problem with 78s
Before the long-playing record, there was the 78: a heavy disc that spun at about 78 revolutions per minute, or rpm, which is simply how many full turns the record makes in a minute.
The 78 was pressed in shellac, a brittle, noisy material, and its grooves were wide. Wide grooves spinning fast eat up space quickly. Even a 12-inch 78 held less than five minutes of music on a side.
For a three-minute song, that was fine. For anything longer, it was a nuisance. A symphony had to be chopped into chunks and spread across a stack of discs, and listeners had to get up every few minutes to flip or change records, right in the middle of the music.
If you wanted longer records, there were two obvious levers. Spin the disc more slowly, or squeeze the groove in tighter. As it turned out, the slower speed had already been worked out. By the film industry.
A disc as long as a reel
In 1926, Warner Bros. released Don Juan, the first feature to use a sound system called Vitaphone. The film itself carried no sound. The soundtrack came separately, on large phonograph records played on a turntable that was mechanically linked to the projector, so picture and sound stayed in step.
That set a very particular requirement. A disc had to keep playing for as long as a reel of film lasted, which was about 10 minutes: one 1,000-foot reel of 35mm film. A 78 couldn't come close.
So the Vitaphone engineers did both of the obvious things. They made the discs much bigger, 16 inches across, and they slowed them right down, to 33⅓ rpm. One side of a disc, one reel of film.
That's where the strange number comes from. It was a cinema standard, set by the length of a reel.
A second life on the radio
Talking pictures soon moved the sound onto the film itself, and the big discs faded from cinemas. But the speed didn't disappear.
Radio picked it up. By the 1930s, recorders for what were called transcription discs were common at larger radio stations. These were big discs, around 16 inches across, spinning at 33⅓ rpm and holding about 15 minutes of sound. Producers recorded programmes on them and sent copies to other stations to broadcast later.
So by the 1930s, 33⅓ was a well-trodden speed. Engineers knew it worked. It just hadn't worked at home.
The false start
It wasn't for want of trying. In September 1931, RCA Victor launched what it called Program Transcription discs: records for the home that spun at 33⅓ rpm with a finer groove, and played for up to 15 minutes a side.
They flopped, and the idea was quietly dropped. The man who shut that project down at RCA Victor was an executive named Edward Wallerstein. He would later try again, somewhere else.
1948: the album arrives
By the 1940s, Wallerstein was running Columbia Records. Columbia had a team working on a long-playing disc, with the engineer Peter Goldmark overseeing the project.
The speed they settled on was the old film speed, 33⅓ rpm. What changed was everything else. Instead of brittle shellac, the new discs were pressed in vinyl, which is tougher and much quieter. And instead of wide grooves, they used what Columbia called microgroove: grooves so fine they were played with a stylus whose tip was rounded to a radius of only about a thousandth of an inch.
Slow speed plus fine grooves meant you could pack an enormous amount onto a disc. In June 1948, Columbia unveiled the long-playing record, or LP, at a press event in New York. A 12-inch LP held around 23 minutes a side, close to three-quarters of an hour of music on a single record. Columbia's own catalogue boasted that it held roughly six times as much as a conventional shellac record.
The first LP in the catalogue was Mendelssohn's Violin Concerto. A whole concerto, no getting up halfway through.
Why exactly a third?
Here's the part I'd love to tell you with confidence, and can't.
Why 33⅓, rather than a round 30 or 35? You'll often read that the figure fell neatly out of the gearing on the electric motors of the day. That may well be true, but we haven't found a primary source that settles it, so treat it as a plausible story rather than a fact.
What is well documented is the reel. The Vitaphone engineers needed a disc to last about 10 minutes, and 33⅓ on a 16-inch disc did the job. Everything after that was inheritance.
The rival that didn't replace it
Columbia's rival had its own answer. In 1949 RCA Victor introduced a 7-inch vinyl disc that spun at 45 rpm. For a while the two formats competed, and the 45 did win something. By the mid-1950s it had become the main format for new songs, and the old 78 was on its way out.
But for longer music, the LP stayed. That's why so many turntables still carry both numbers on the switch: 45 for the single, 33⅓ for the album.
What the album remembers
There's something lovely about the chain of events here. Nobody sat down and asked how long an album side ought to be. A film reel ran for about 10 minutes. A disc was slowed down to match it. Radio kept the speed alive. And when Columbia wanted a record that could hold a symphony, the speed was already there, waiting.
So the next time you flip an LP after twenty-odd minutes, it's worth a thought. The length of that side, and the shape of the album as we know it, owes a quiet debt to the running time of a reel of film in 1926.
Sources
Library of Congress, Now See Hear!, "Inside the Archival Box: The First Long-Playing Disc" (April 2019). https://blogs.loc.gov/now-see-hear/2019/04/inside-the-archival-box-the-first-long-playing-disc/ (accessed 1 Nov 2026)
Wikipedia, "LP record" (cross-check; sole source for the microgroove stylus radius). https://en.wikipedia.org/wiki/LP_record (accessed 1 Nov 2026)
Mix, article on early film sound and Vitaphone (16-inch discs at 33⅓ rpm, about 10 minutes, one 1,000-foot reel). https://www.mixonline.com/?p=83776 (accessed 1 Nov 2026)
Ingenium (Canada Science and Technology Museum), "Record, disk" (16-inch, 33⅓ rpm Vitaphone sound-film disc, 1926–1930). https://collections.ingenium.ca/en/id/1990.0150.011/ (accessed 1 Nov 2026)
Engineering and Technology History Wiki, "Sound Motion Picture Technology". https://ethw.org/Sound_Motion_Picture_Technology (accessed 1 Nov 2026)
UMKC University Libraries Special Collections, "Content sharing in the '30s" (transcription discs). https://info.umkc.edu/specialcollections/archives/3111 (accessed 1 Nov 2026)
Classic 45s, "A Brief History and Some Background" (the 45 and the 78). https://www.classic45s.com/blogs/the-joy-of-45-collecting/a-brief-history-and-some-background (accessed 1 Nov 2026)
