Unit Definition (Teaspoon [metric])
The teaspoon is a unit of volume used in food recipes. In metric kitchens in Britain, Canada, Australia, and New Zealand, a teaspoonful is exactly 5 milliliters.

Unit Definition (Teaspoon [UK])
The teaspoon is a unit of volume used in food recipes. In Britain, a traditional teaspoonful in the kitchen was equal to 1/8 Imperial fluid ounce or approximately 3.55 milliliters, but the medical teaspoonful was usually 5 milliliters.