*By Richard Bloch*

If you have any old rolls of pennies around, you might want to dig them out and weigh them.

Although copper has backed off a bit from its recent high of $4 per pound, US pennies minted before 1983 are actually worth a lot more than a penny – at least in terms of copper.

Currently minted pennies contain very little copper (they’re mostly zinc), but by my calculations, those pre-1983 pennies could be worth a bit more than 2.3 cents each.

I should point out that it’s currently illegal to melt these coins, or even export them, but you might want to hold onto them anyway.

Although I haven’t actually weighed any coins, here’s how I think you could tell whether a roll of pennies is rich in copper.

When minted, the pre-1983 pennies weighed 3.11 grams, but the newer pennies weigh only 2.5 grams. Allowing about 1.5% for wear, I’m assuming that a 95% copper coin would weigh about 3.06 grams. Newer coins probably haven’t worn out much, so let’s assume they still weigh 2.5 grams.

Theoretically, the number of copper-laden pennies in a roll could range between 0 and 50. So here’s what various rolls of coins could weigh.

*click to enlarge*

The total column height represents the total weight of the roll, so it’s higher when it contains more of the heavier 95% copper coins. A full roll of those coins would weigh more than 150 grams, but only 125 grams if it contained only the newer pennies.

(I suppose a roll could contain some of those 1943 steel pennies, but I’m just going to ignore that possibility for now.)

As for value, with copper trading at around $3.73 per pound this mid November, here’s what these theoretical rolls of pennies could be worth in terms of copper content, plus 1 cent for each of the mostly zinc coins.

I don’t have any rolls of pennies around – and I’m not even sure it’s practical or worth the effort to see which might contain more copper. After all, you’d need to find almost 4,200 of these pennies to have the equivalent of $100 in copper.

But if someone offers you a “penny for your thoughts,” check to see if it’s one of those copper pennies first. Getting 2.3 cents for only a penny’s worth of thinking could be a great deal.