When it comes to cooking measurements, a pinch is generally equal to about 1/8 of a teaspoon. Measurement amounts that are not specific, such as pinch, bunch, sprig, dash and generally leave the judgment of how much to add to the dish to the cook. For example, some people do not like much seasoning in their dishes while other like to add more.
Some websites, such as Gourmet Sleuth, offer a conversion calculator that makes determining how much of something to add to a recipe much simpler. For example, a drop is equivalent to .013 of a teaspoon or .211 of a dash. The site also offers a metric conversion calculator as well.