To calculate a coin's base price, or silver value, you need to know how many ounces of the precious metal it contains. Then you can compare its silver value with a coin dealer's price to know how much of a premium you would pay for the coin. Pre-1965 U.S. dimes, quarters, half dollars and silver dollars, as well as silver state quarters, contain silver that is 90 percent pure. American Silver Eagle bullion coins are nearly 100 percent pure. The amount of pure silver in each coin varies by denomination.

Look up the spot price, or current market price, of silver. Because the price varies, we'll use a hypothetical spot price of $16 per troy ounce for our calculations.

Calculate the silver value of a pre-1965 dime. The U.S. Mint produced three versions of the dime in the 20th century: the liberty head, or "Barber," named for U.S. Mint engraver Charles E. Barber; the winged liberty head, or "Mercury"; and the current Roosevelt design. To calculate the silver value, multiply the hypothetical $16 spot price by the amount of precious metal that a 90 percent silver dime contains, 0.0723 troy oz. The dime would be worth $1.16 before the coin dealer's premium.

Determine the silver value of a pre-1965 quarter. The 20th century quarters carried the Barber, standing liberty and Washington designs. By multiplying the hypothetical spot price by the amount of silver in a quarter, 0.1808 troy oz., you'll find that one of these coins, or a silver state quarter, would be worth $2.89 based only on its silver content.

Calculate the silver value of a pre-1965 half dollar. The U.S. Mint produced four designs for this coin in the 20th century: the Barber, walking liberty, Franklin and Kennedy. Among the Kennedy half dollars, the 1964 coin is the only regular-circulation version that is 90 percent silver. Multiply the $16 spot price by 0.3617 troy oz. and you'll see that these coins would be worth $5.79 each.

Find the silver value of a pre-1965 silver dollar. The 20th century versions were the Morgan silver dollar, named for its designer, George T. Morgan, and the peace dollar. Multiplying the hypothetical spot price by 0.7734 troy oz. reveals that the silver in one of these coins would be worth $12.37.

Calculate the silver value of an American Silver Eagle. These silver bullion coins, which the U.S. Mint has produced since 1986, contain 1 troy oz. of 99.9 percent pure silver. Therefore, the noncollectible version that coin dealers sell would be worth $16.

Calculate the coin dealer's premium. Subtract the coin's silver value from the dealer's price. For "junk silver," or coins that are too worn or widely available to have collectible value, the premiums vary based on supply and demand, and how many ounces you are buying. Premiums for collectible coins may eclipse their silver value by hundreds or even thousands of dollars.