United States pennies minted after 1982 weigh 2.5 grams, or 0.088 ounces. These pennies are 2.5 percent copper and 97.5 percent zinc. Before 1982, pennies weighed 3.11 grams, or 0.110 ounces. They were 95 percent copper and 5 percent zinc, which is a form of bronze.
During 1982, the U.S. Mint issued pennies of both compositions, and both 2.5-gram and 3.11-gram pennies can be found in circulation. The weight of the penny also changed in 1943. Because of a scarcity of copper, pennies were minted from zinc-coated steel. These weighed 2.7 grams, or 0.095 ounces. Other small changes in design and metal composition have been made over the last hundred years, but they have not changed the weight of the coin except as already described.