A dram is a unit of measurement from the old apothecaries’ system, equal to 60 grains or roughly 3.89 grams by weight. In liquid form, one fluid dram equals about 3.7 milliliters, or one-eighth of a fluid ounce. While the metric system officially replaced the apothecaries’ system in the United States in 1971, the dram lives on in one very visible place: the sizing of prescription pill bottles.
Weight Dram vs. Fluid Dram
The dram actually refers to two related but distinct measurements. The weight dram (sometimes spelled “drachm”) measures mass: one dram equals 3 scruples, each scruple containing 20 grains, for a total of 60 grains or 3.89 grams. Eight drams make one apothecaries’ ounce, and 12 of those ounces make one apothecaries’ pound.
The fluid dram measures volume. One fluid dram equals one-eighth of a fluid ounce, which works out to approximately 3.7 milliliters. This is the version you’re most likely to encounter today, since prescription vials are still labeled and sold in dram sizes.
The Apothecaries’ System It Came From
The dram belonged to a complete measurement system built specifically for pharmacy. The apothecaries’ system was the standard for measuring and dispensing medications across the British Isles and the United States for centuries. Its units scaled up neatly: grain, scruple (20 grains), dram (3 scruples), ounce (8 drams), and pound (12 ounces). Notice that last number: the apothecaries’ pound contained 12 ounces, not 16, which set it apart from the everyday avoirdupois system used in groceries and commerce.
That distinction matters because there’s also an avoirdupois dram, and it’s a completely different weight. The avoirdupois dram equals only 27.34 grains (1.77 grams), roughly half the size of the apothecaries’ dram at 60 grains (3.89 grams). Confusing the two could mean a significant dosing error, which is one reason the pharmacy world eventually moved away from the system entirely. Great Britain adopted the avoirdupois system for dispensing in 1858, then switched to metric in 1963. The United States followed in 1971.
The Dram Symbol and Why It Caused Problems
Pharmacists once used a special symbol for the dram on handwritten prescriptions. The character resembles a lowercase “z” with a tail, derived from the medieval English letter yogh. In practice, it looks almost identical to the number 3. The Institute for Safe Medication Practices lists the dram symbol on its official roster of error-prone abbreviations for exactly this reason: a prescriber writing the dram symbol could easily have it read as the numeral 3, potentially leading to incorrect quantities or doses.
ISMP’s recommendation is straightforward: use the metric system instead. Modern prescriptions are written in milligrams, milliliters, and grams, eliminating the ambiguity that old apothecary notation introduced.
Where Drams Still Show Up Today
Walk into any pharmacy and you’ll find the dram still in daily use, just not for measuring drugs. Prescription vials, the amber plastic bottles your pills come in, are sized and sold in drams. Standard sizes range from 6 dram (about 22 milliliters of capacity) up to 60 dram. Pharmacists and pharmacy technicians choose the vial size based on how many tablets need to fit inside, which depends on the length of the prescription, the physical size of each pill, and the total quantity dispensed.
A 13-dram vial is a common choice for a typical 30-day supply of small tablets. Larger medications, higher quantities, or 90-day supplies call for 30-, 40-, or 60-dram vials. If you’ve ever noticed a number printed on the bottom of your prescription bottle, it may indicate the dram size.
Quick Conversion Reference
- 1 dram (weight): 3 scruples, 60 grains, 3.89 grams
- 1 fluid dram: 3.7 milliliters, one-eighth of a fluid ounce
- 8 drams: 1 apothecaries’ ounce
- 1 avoirdupois dram: 27.34 grains, 1.77 grams (the non-pharmacy version, roughly half the apothecaries’ dram)
For pharmacy students or technicians studying for certification exams, the apothecaries’ system still appears in coursework as historical context. In practice, though, every modern prescription and compounding formula uses metric units. The dram’s most lasting legacy is the humble pill bottle.