According to the dictionary, the term bullion technically refers to gold and silver in bulk, in the form of bars, ingots, and rounds. In practice, investing in coins with a composition of 90 percent or more silver can also be considered a form of investing in silver bullion.

Silver bullion is often available in bars and rounds of one troy ounce each. The advantage of single ounce bars and rounds is that a single ounce of silver is affordable for many small investors, and investors can build up their investment in small increments. Silver bullion bars of 10 ounces are also popular.

Silver bullion bars of 100 and even 1,000 ounces can also be found. For those investing in silver bullion with the intention of remaining active in the market, 100 ounce bars are a practical choice because they dominate the retail market. Bars of 1,000 ounces can be held as a retirement investment.

Silver coins can also function as an investment in bullion. The United States Mint makes bullion coins (the American Eagle series) of gold and silver (one ounce) that are easily bought and sold through coin and precious metals dealers. Some people also consider pre-1965 common US coins (dimes, quarters, and half dollars) to be a form of bullion investment because they are composed of 90 percent silver.

When melted down, these older circulating coins with a face value of $1,000 will yield around 715 to 720 ounces of pure silver.