The length of a glove is traditionally expressed in buttons, an antique French unit of measure which is slightly longer than one inch. Button measures are customarily taken from the bottom of the thumb seam to the top of the glove.
The various traditional lengths are:
2-button Also known as shorties. These are wrist-length gloves, generally 8 to 9 inches long.
4-button These gloves are 10 to 11 inches long and cover the wrist, reaching a couple of inches up onto the forearm.
6-button 12 to 13 inches long, these gloves reach well up onto the forearm. Many gauntlet type gloves (i.e., these gloves with flared armpieces in the style of equestrian gauntlets) are this length.
8-button 14 to 15 inches long, this type of glove reaches to the upper forearm. This is also known as the "three-quarter" length glove
12-button Approximately 18 to 19 inches long, this type of glove reaches up to and just over the wearer's elbow. Known as elbow-length, many have wrist openings (called mousquetaire).
16-button 22 to 23 inches long - this is the classic Opera length, and as a general rule comes with the wrist opening.
21-button 27 to 29 inches long, the very longest of the glove length. This glove generally reaches all the way to the wearer's armpits. This is generally worn only with strapless or sleeveless evening outfits.