A dram is a unit of mass that is equal to either 1/16 ounce, 1.77 grams in the avoirdupois system of measurement or 1/8 ounce in the apothecaries' system. The related unit of measurement is the fluid dram, and it is used to measure volume.
As a unit of volume, a fluid dram is equal to 1/8 fluid ounce in the U.S. system of measurement and 3.55 milliliters in British Imperial units. The measurement of a dram may also be used informally to refer to a small amount of some types of liquor. A dram is sometimes called a drachma. A teaspoon is equal to 1 1/3 fluid drams.