One tenth of a teaspoon equal?

In some countries, the teaspoon is used as a unit of volume, especially in cooking recipes and pharmaceutic prescriptions. It is abbreviated in English as t. or tsp., German and Dutch: TL, from Teelöffel or Theelepel. A teaspoon is often taken to mean 5 millilitres. 1 tenth of a teaspoon is 0.5 millilitres of volume. Don't use it as a weight.