Drams and Gills

This diagram from the Columbia Gorge Discovery Center and Museum in The Dalles, Oregon, shows the comparisons between drams, ounces and gallons.

It’s often mentioned in the Lewis and Clark journals that whiskey was rationed out by the gill or dram. Joseph Whitehouse wrote on June 9, 1805, “…the officers gave the party a dram, the fiddle played and they danced late &c…”

How much was a gill? The Oxford English Dictionary defines a gill as "a measure of liquids containing one fourth of a standard pint." Thus, at one-fourth of a pint, a gill equates to four ounces. With two pints to the quart and four quarts to the gallon, there are 32 gills to the gallon.
A fluid dram equals one-eighth of a fluid ounce (the equivalent to two average-size thimbles), so there would be 128 drams per pint and 1,024 drams per gallon. So, there are 32 drams in a gill.