The standard size of a gold bar is 400 troy ounces. This is known as a Good Delivery bar and is the size used by central banks to store gold reserves, as well as by dealers for trading purposes. 400 ounces is the nominal weight of a Good Delivery bar, not the gold weight contained therein; the actual weight is permitted to range between 350 and 430 ounces, but must be at least ninety-nine and a half percent pure. Additionally, there are storage requirements that permit these bars to maintain their status as Good Delivery. They must be stored in certified vaults like Via Mat which is used by Bullionvault, but this ensures that their resale value is maintained.
In addition to helping ensure that market participants receive the actual product for which they have contracted, maintaining this type of standard helps to ensure the orderly operation of the market. While the gold standard has not been used for decades, many central banks continue to hold reserves in the form of gold. The precision with which these reserves can be measured is valuable in maintaining the bank's credibility. Additionally, as bullion dealers will regularly use this size to effectuate transfers, maintaining a known set of standards promotes the smooth flow of business.
While most investors will not transact in Delivery bars, as this represents over $700,000 at current spot prices, given how bullion is stored, it is important in maintaining confidence. Gold is typically owned in two ways, as an allocated holding and as an unallocated holding. In the former case, the specific physical gold is held in the investor's name. In the later case, a general stockpile of gold is held against the investments of various investors, but specific bars are not assigned. With an unallocated investment, it is of the utmost importance that investors have confidence in the quality, weight and purity of the gold that backs their capital. Without this confidence, the market could not function efficiently. You can visit the links below to buy gold bars or learn more information about the subject.