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I came up with a quick formula to determine how many 95% copper cents are in a roll, without even opening up the roll itself.
Weigh the individual roll using a jewelry scale, set to grams. Take that number and subtract 126. Then divide that number by 0.61. The sum will be the number of 95% copper coins in that roll!
Here is the reasoning behind the formula using what we know:
A single 95% copper cent weighs 3.11 grams.
A single newer type of copper-plated zinc cent weighs 2.5 grams.
We will assume the paper used to wrap the roll weighs 1 gram.
Therefore, we know that a full roll of 95% copper cents wrapped in paper will weigh 156.5 grams. (3.11 x 50) + 1 = 156.5
We also know that a full roll of copper-plated zinc cents wrapped in paper will weigh126 grams. (2.5 x 50) + 1 = 126
Using this information, I take a random roll and weigh it. The scale reads 132.71 grams.
How many 95% copper cents should be in this roll?
First, subtract the total from the base, 132.71 - 126 = 6.71
Then divide this remainder by the constant 6.71 0.61 = 11
There should be 11 total 95% copper coins in this roll, and sure enough, that's what I find!
As a side note, this formula doesn't account for a roll that might contain 1943 steel cents, and if cents have worn a bit due to circulation, in that case, you can round up to determine the final number. On the odd chance you find a roll that weighs more than 156.5 grams, you might have struck silver or gold.
Happy copper hunting,
Jared Grove
Founder & CEO
Grove Minting Company
"Originally published November 2014"