← All scales
Hierarchy
The Apothecaries' Fluid Measure
Liquid medicine measured down to the drop.
Origin
Standardised in the London Pharmacopoeia of 1809 and carried into the imperial system in 1824.
The catch
The minim was defined as one drop, but a drop varies with the liquid and the vessel. Fixing it at one sixtieth of a fluid drachm turned an approximation into a number, which is precisely what pharmacy needed and folk medicine never had.
Minim0.0592 ml
× 60roughly a drop, made exact
Fluid drachm3.552 ml
× 8
Fluid ounce28.41 ml
× 20
Pint568.26 ml
The scale runs neatly into the ordinary imperial system at the fluid ounce, which is why a pharmacist and a publican could share a pint while disagreeing about everything below it. The fluid drachm is frequently confused with the Scottish whisky dram, which is roughly ten times larger and belongs to an entirely different tradition.