If you are thinking of buying gold as an investment then please learn the units of weight used. Some sellers rely on the fact that most people have never heard of the Troy or apothecary's units of weight used in the precious metal markets and it is easy to confuse the unwary.
1 grain is 1/480 of a troy ounce
1 gram is 1/31 of a troy ounce (1/31.1035 to be precise)
There are 480 grains in one troy ounce and 15.43 grains to a gram
There are 31.1035 grams in one troy ounce.
There are 28.349 grams in 1 oz avoirdupois
There are 437.5 grains in 1 oz avoirdupois
Interestingly and this is where it can get even more confusing. When we are talking about precious metals 1 Troy pound is 12 troy ounces (12x480) which is 5760 grains. While 1 pound avoirdupois is 16oz avoirdupois (16x437.5 = 7000 grains). So even though a troy ounce is heavier than an avoirdupois ounce, a troy pound weighs less than an avoirdupois pound.
As I said confusing for the unwary. Don't get caught out. The difference between a troy and avoirdupois ounce as of 11/11/11 is about £107.00