All vinyl records in the USA are manufactured according to the standards specified by the RIAA (Record Industry Association of America). That being said, the sizes of different kinds of records, in inches, do not translate to the actual measurement of the diameter, but are sort of trade names adopted for convenience. For example, a 12" LP record has an actual diameter of 11.89 inches (302 mm), and not 12 inches.

Before vinyl records came into use, the ones made of shellac, which is a kind of abrasive wax, were the prevalent format for musical recordings. These discs were typically 10" or 12" in size, and rotated at a speed of 78 rpm (revolutions per minute). In the post-WW2 days, shellac records began to be called the '78s' to distinguish them from the newly introduced vinyl records, which came in similar sizes. A "78" could hold around 4 or 5 minutes of music on one side in the case of a 12" disc, and up to 3 minutes in the case of a 10" disc. Obviously, for longer music tracks, this limitation called for frequent disc replacement, and the idea of recording or listening to an entire album from a single disc was entirely unheard of. The practice of manufacturing records made of vinyl was adopted because of the material's low cost (it is basically a plastic called PVC), and also because vinyl was less susceptible to breakage than shellac. Vinyl records too, were manufactured in sizes similar to their predecessors. Since the 1930s, the project of developing records and record players that could achieve longer playback had been undertaken by a number of record companies, but unfortunately because of the Great Depression, most of these attempts had to be put aside. Finally in 1948, Columbia Records, with the release of their first microgroove Long Play (LP) record, heralded the commercial viability of this format. Technically speaking, the recording of music on discs is achieved by etching the audio signals on to the tiny grooves present on both the surfaces of record discs. LP records contained grooves having a size of the order of millimeters, and hence, they had a much greater capacity to hold music than previously prevalent records. One side of a 12" LP record could hold up to 22 minutes of music, which meant that the entire disc could hold up to 45 minutes of music. A 10" LP disc could hold up to 35 minutes of music altogether. These discs rotated at a speed of 33½ rpm. Apart from soon becoming one of the leading standards in the music industry for recording full albums, LP discs proved to be ideal for classical music because of their increased capacity as compared to their forerunners, the 78s. They were also commonly used for Broadway musicals. This name was given to another kind of vinyl record that rotated at 45 rpm. These discs were developed and manufactured originally by RCA Records. They were produced in many different sizes, with different music-holding capacities: ♦ The 12" 45 rpm disc that could hold up to 15 minutes of music on one side were direct competition for 12" LP records. ♦ 45s were also released as 7" and 10" discs. The 7" 45 rpm records were also known as single records, as they commonly carried singles released by artists. They could hold up to 5 minutes of music per side. ♦ The 10" 45 rpm records, on the other hand, were called Extended Play, or EP records. Their music-holding capacity was around 10 minutes per side. EP records could hold more than a single track, but less music than a full album, owing to its reduced capacity.

The terms LP and EP have a slightly different meaning when looked at from the point of view of the format for a music album, as opposed to that of the physical media (gramophone records) used to store music.