Since milligrammes are a weight measurement and teaspoons are a volume measurement, it is not possible to simply convert between them. In order to convert milligrammes to teaspoons, it is important to know the density of the substance being measured. The density of water, for instance, is 1 gramme per millilitre, therefore 0.2 grammes of water = 0.2 millilitres, or 0.04 teaspoons of water.
A gramme contains 1,000 milligrammes, so 200 milligrammes = 0.2 grammes. The density equation is mass divided by volume. To convert mass to volume, simply divide the mass by the material’s density. For instance, the density of butter is around 0.9 grammes per millilitre, so 0.22 millilitres of butter is equivalent to 0.2 grammes of butter divided by 0.9 grammes per millilitre. The volume of 200 milligrammes of butter is 0.22 millilitres. This result still requires conversion to the imperial system. A teaspoon contains 5 millilitres. To convert millilitres to teaspoons, divide by 5. Therefore, 0.22 millilitres of butter divided by 5 = 0.04 teaspoons of butter. 200 milligrammes of butter is equivalent to 0.04 tablespoons of butter.