By Duane Thomas
As you learn more about firearms, and measurements of bullet weight, and powder charge weights, you discover they’re measured in grains. Also eventually, you will discover there are 437.5 grains in one ounce. WHY? How did we come up with the idea that 437.5 grains equals one ounce? Why, I’m glad you asked!
The “apothecary” system was formalized in Europe during the Middle Ages, specifically around the 15th Century. It was mostly used by apothecaries (pharmacists) for measuring medicinal ingredients where small differences in the amount of an included ingredient could have profound effects.
Developing roughly concurrently with, possibly slightly before, the apothecary system we also had the “avoirdupois” system, with the term coming from the Old French “aveir de peis,” meaning “goods of weight” or “property by weight.” The avoirdupois system was more coarse and less precise in its measurements than the apothecary system, and more suited for bulk goods like foodstuffs, base metals, and textiles. It was used for most things other than high-value items like precious metals and gems, or where precision was an overriding concern such as the amount of ingredients in drugs
The avoirdupois system was formally standardized in England during the 14th Century. A need existed to define how these two systems, apothecary and avoirdupois, interacted. It wasn’t until the 19th Century that a clear relationship between the two was established.
The avoirdupois ounce was initially defined in relation to the pound. A pound was standardized at 7,000 grains, which was then divided into 16 ounces.
Why 16 ounces to a pound? The idea of dividing a pound into smaller units called ounces was already in existence from the Roman system of measurement, though the Roman system used 12 unciae (ounces) per pound. It was decided that 16 ounces made more sense. 16 is a highly-divisible number in base 2 (which means it’s divisible by 8, 4, 2 and 1 where easy succeedingly-smaller fraction is exactly one-half of the previous amount) whereas 12 is divisible by 6, 4, 3, 2 and 1 (in other words, not in base 2) making 16 ounces convenient for splitting into various, consistently smaller units for trade, especially in markets where goods could be sold in fractions of a pound.
Thus:
1 pound = 7,000 grains
1 pound = 16 ounces
1 ounce = 7,000 grains / 16 = 437.5 grains
1 ounce = 437.5 grains
This conversion was legally set in various countries over time through laws like Britain’s Weights and Measures Act of 1824, and the United States’ Weights and Measures act of 1836. Thus the avoirdupois system was adopted in the United States and other countries, solidifying the 437.5 grains per ounce measure.
The choice of 437.5 grains for an ounce reflects a balance between convenience (divisibility by whole numbers in base 2 for practical use) and the existing standards of weights at the time. This system allowed for practical, everyday measurements while maintaining a level of precision in trade and commerce.
The exact rationale for choosing 437.5 grains might also have been influenced by existing scales and the need for ounce measurements to integrate smoothly with the already established weight system of grains used for smaller, more-precise measurements. This system persists due to its adoption in industrial and commercial contexts, where continuity in standards was, and is, crucial for trade and manufacturing.
Bottom line, in the apothecary system we had grains. In the avoirdupois system we had ounces. Therefore, over time we simply had to know how many grains there were in an ounce, and when all was said and done, the answer turned out to be 437.5.
