Fifteen milliliters is equivalent to 3 teaspoons, while 4 teaspoons equals 19.716 milliliters. The metric system includes three basic units of measurement: gram (weight), meter (length) and liter (volume). The United States is the only industrialized country that does not recognize the metric system as a universal measurement system.
Metric units used for cooking and baking include the milliliter, liter, gram, kilogram, centimeter and millimeter. Most glass or plastic liquid measuring cups provide metric conversions on the sides, according to The Metric Kitchen. Small kitchen scales provide accurate metric weight conversions, for example, ounces to grams. Measure all dry and liquid ingredients using measuring cups, spoons and scales to ensure proper taste and appearance of food.