Drop (unit)

Drop (unit)

The drop is a unit of measure of volume, the amount dispensed as one drop from a dropper or drip chamber. It is often used in giving quantities of liquid drugs to patients, and occasionally in cooking.

The volume of a drop is not well-defined: it depends on the device and technique used to produce the drop, on the strength of the gravitational field, and on the density and the surface tension of the liquid.

There are several exact definitions of a "drop":

• in medicine, IV drips deliver 10, 15, or 20 drops per mL for macrodrip, 60 per mL for microdrip
• an informal (and incorrect) synonym for minim, the smallest unit of fluid measure in the Apothecaries' systems of the United States customary units, Imperial units, and pre-1824 English units equal to 1/60 of a fluid dram or 1/480 of a fluid ounce
• prior to the adoption of the minim in the early 19th century, the smallest unit of fluid measure in the Apothecaries' systems of the United States customary units and pre-1824 English units, inexact, but presumed to be equal to 1/60 of a fluid dram or 1/480 of a fluid ounce