If a recipe calls for "a dash" of an ingredient, it is somewhat relative. However, the most accurate amount appears to be 1/16-teaspoon. Basically, you just add the ingredient "in a dash". For example, if it is a dry ingredient, such as a spice, just shake the box once, assuming there are small holes, and what comes out is it. It's the same with liquid ingredients that come out in drops. Remember, many of those types of ingredients are to taste, so a tiny bit more or less won't matter.