If you’re into vinyl, you may have asked yourself “Why is this album I’m holding twelve inches in diameter?” That’s a valid question.
When inventors were experimenting with flat discs for recording sound more than a hundred years ago, they tried a number of diameters ranging from three inches to five to seven to eight to ten to twelve to fourteen to even sixteen. When the 78 RPM record was introduced, ten inches seemed to be the right balance for speed and capacity.
But in 1948, Columbia Records introduced the long-playing record which could hold more than one song per side. To balance the needs of capacity (minutes of music per side) with speed (33 1/3 RPM) with the size of grooves required (they were called “microgrooves), everything came together in a size that said “twelve inches.” And so it stuck.