The average penny minted after 1982 weighs 2.5 grams. 28-30 = 1 ounce......14-15 to half an ounce...7 to a quarter ounce and i would say about 4 pennies to an eighth....remember you can't get it exact using pennies so just try to get it close...that's by weight....it wouldn't be a good idea to measure by the volume...since that can vary greatly....