The tablespoon began as a soup spoon and changed size by country
A tablespoon is exactly 15 millilitres in Britain and the United States, but 20 in Australia, where it also equals four teaspoons rather than three. The spoon itself has an odder history: it started as the soup spoon of the new European place setting and ended up, in Britain, as a serving spoon.
Until about 1700, Europeans brought their own spoons to meals, carrying them as personal belongings the way people now carry keys. Around then the matched place setting caught on, bringing the table-spoon, table-fork and table-knife, along with the first teaspoons and dessert spoons. The table-spoon was meant for soup.
In late 19th-century Britain the dessert spoon and soup spoon took over eating from bowls, and table-spoon drifted toward meaning a much bigger serving spoon. When the first edition of the Oxford English Dictionary appeared in 1928, the word had lost its hyphen but still carried both meanings. Victorian and Edwardian serving tablespoons often hold 25 mL or more, while the spoons British diners actually eat with, called dessert spoons there, usually hold 7–14 mL.
As a measure, the definitions have wandered. The old American customary tablespoon was about 14.8 mL, half a US fluid ounce, and the old British one about 14.2 mL, half an imperial fluid ounce. Australia's Metric Conversion Board fixed its own 20 mL standard in the 1970s during metrication, without creating matching teaspoons or dessert spoons. In the 18th century the table-spoon even served apothecaries as an unofficial unit of 4 drams, usually written in Latin as cochleare majus.
Recipes shorten the word to tbsp., and some writers capitalise it as Tbsp. so cooks do not mistake it for the teaspoon; Tb. and T. also turn up. A level spoonful of a dry ingredient is scraped flat, while a heaped one keeps a mound on top, so its volume depends on the curve of the spoon and on whatever is being measured.
Source: Tablespoon
