Junksilverbook.com has several calculators to make it easy to do the math on junk silver.
Junk Silver Calculator will calculate the value of any junk silver (pre-65 90%, silver dollars, 40% halves, war nickels, silver Eisenhower)
Basic Pre-65 90% Junk Silver Calculator is a basic calculator for only pre-65 90% silver dimes, quarters, and halves.
Multiplier Calculator will calculate junk silver face multipliers for a given silver price per ounce, or calculate the silver price per ounce for a given multiplier
Gold Coin Calculator will calculate the gold content and intrinsic value of pre-33 U.S. gold silver coins