A Basic Guide to Weights and Measures for Coins

A Basic Guide to Weights and Measures for Coins
Sometimes coin collectors get very confused when they look at coin specifications in coin publication or advertisements. It just doesn’t make any sense. I have spent hours on the phone with some of my clients helping them to understand all the technical jargon. What we are going to do is to make it simple. I firmly believe the simple way is the best way. Once you grasp a couple of basic rules, the rest is easy.


In discussing the weight or mass of a coin, especially in US versus foreign, or old US versus the new US Bullion coins (the silver, gold and platinum eagles), we need to know what system of weight measure with which we are dealing. Metals are mostly weighed by the Troy system. We, in the United Sates, use the Avoirdupois system. Is there a difference? The answer is – YES! Don’t worry about trying to convert one to the other, just remember a few basic weights, and that will allow you to grasp the general concept with which you are dealing.

We were taught in school, as I remember around 5th grade, the following Avoirdupois weights:

1 ounce = 437.5 grains
1 ounce = 28.35 grams
1 pound = 16 ounces
2.2 pounds = 1 Kilogram

The Troy weight system is a little different, but not much, the units of grains and grams are the same in both the Avoirdupois and the Troy weight systems, so here we go:

1 ounce Troy = 480 grains
1 ounce Troy = 31.103 grams
1 pound Troy = 12 ounces Troy
2.7 pounds Troy = 1 Kilogram

That’s pretty simple. One last conversion you might want to commit to memory is:

1 pound Avoirdupois = 14.583 ounces Troy


All coin diameters are measured in the metric system, i.e. millimeters. I can hear you groaning already. You are trying to remember that 1 inch equals 25.4 mm, and how to do the conversion. Forget it. Forget all of it. Let’s make it simple for you. Remember the dimensions of just 6 US coins and the rest is easy, and equate everything else to them.

Lincoln cent = 19 mm
Jefferson Nickel = 21.2 mm
Roosevelt Dime = 17.9 mm
Washington Quarter = 24.3 mm
Kennedy Half Dollar = 30.6 mm
A Silver or an Eisenhower Dollar = 38.1 mm

So far, so good? There will be a test at the end.


Coins are generally made of an alloy. The mint mixes other metals into the coin so it will last longer, just like in jewelry. Where jewelry uses the measure of karats to describe its purity or fineness, with coins, there is a decimal system used.

If a coin has a fineness of .900 fine silver, we move the decimal point two places to the right, add a percent sign to the number, and we have a coin that is 90.0% pure silver. If a gold coin has a fineness of .999, then the gold coin is 99.9% pure. Pretty simple!

So, here is your test. You see an advertisement for a 2005-year dated, French gold coin. It is 15.05 grams in weight, 26 mm in diameter with a .9999 fineness. What do you have?

A ½ Troy ounce coin, slightly larger then a quarter, and it is 99.99% pure gold.

I’m sure you all got it correct. Weights and measures made simple.

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This content was written by Raymond F. Hanisco. If you wish to use this content in any manner, you need written permission. Contact Gary Eggleston for details.