How many grams are there in an ounce?

28.

There are 28 grams in a common ounce. This refers to the ounce as a measure of weight, also known as the international avoirdupois ounce. This measurement was adopted by the United States and the Commonwealth of Nations in 1958, when these nations declared that the international avoirdupois pound to be exactly 0.45359237 kilograms.