Interesting question. I guess circulation wear would factor into the equation. There are also "within range" numbers to consider. I use a chart that one of our members provided to see if any US coinage falls over/under acceptable parameters. I guess foreign coinage and ancients are another whole ballpark. I think with me underweights come up the most, due to wear. https://www.cointalk.com/attachments/us-coins-weight-composition-and-tolererances-jpg.1257744/
Underweight. I used to see them all of the time at the coin shop. Mainly silver dollars because they were fakes. Not that people were trying to get away with something. Things they bought thinking they were real. You get to the point where you don't even need to weigh you can just tell because you've handled so many. Then you weigh them anyway.
This is a question or topic that comes up every now and then. And a lot of folks have preconceived notions about it. But the reality is what they "think" is simply not true. For example, yes the US has always had specified weight and purity tolerances for their coins. But what people don't think about is where they (the US) got the idea to do that in the first place - they got it from other countries ! The countries, which at that time, everybody in the US came from. Now it depends on the country, and it depends on the time frame you're talking about, as to what the weight and purity actually were, but as a general rule they even more stringent that those chosen to be used by the US. And as a general rule, the further back you go, the tighter the tolerances get ! And the more modern the coin is the higher the tolerances get. Some folks also think that just because it was a long time ago the people of the time didn't have the ability to accurately regulate things like weight and purity, that they lacked the technology to do this. But this is simply not true ! Mints have had the ability to accurately regulate the weight and purity of coins to 3 and 4 decimal places for 2,000 years. And they were very, very strict about it. Strict to the point of those guilty of cheating and not following the specified tolerances of being put to death ! And quite often in very horrid ways, such as being boiled alive. And yes, all of this is documented. What's more, even when using modern day methods for testing, coins minted 400, 500, 800 years ago are found to be within the specified tolerance ranges of the time. This too is documented. Regarding weight loss from wear. Again, contrary to what a lot of people "think", coins, even those worn down to F and many in VG grade, are still within mint tolerance ranges for weight. In other words, as a general rule coins do not lose weight in any meaningful amount from wear ! At least not until that wear gets to low or below VG grade. And yes that is even true of gold coins. And yes, this too is documented. For example, this coin, and I've posted about this numerous times. What would you guess the grade of that coin to be ? And, how much weight would you guess it lost due to that much wear ? It was my coin, and I weighed it the day I bought it. And then I weighed it again when I took these pictures 7 years later right before I sold it to another forum member. I would grade the coin in the low F range. And the weight, well, that coin lost 0.003 of a gram after that much wear ! Over the years I have weighed many, many coins worn down to this point and lower. And only very rarely was one ever found to be below original mint tolerance weight. As a general rule coins need to be worn to low VG and lower than that before they lose any appreciable weight.
there's mint tolerance, therefore there isn't any underweight or overweight. Until it's out of that tolerance range for the type, it's all acceptable weights.
Not everything MM, I'm within tolerance for my age, according to this year's physical. Scratch one off your list MM, thank you. Be safe up there in God's country.
@JPD3 was nice enough to post a link to a chart with all of the weights and tolerances in post #2. Did you take a look at it?
In my response above I should have added that when weighing coins it is always necessary to check your scale and make sure it is calibrated correctly. They can and do often get out of calibration giving you misleading results.