1 Ounce = 28.3495231 Grams
1 Troy Ounce = 31.1034768 Grams
There are 28.35 grams in an ounce, because by definition 1 kilogram is 2.20462 pounds (equals to 35.27392 ounces) and there are 1000 grams in a kilogram, that makes 1000 / 35.27392 = 28.35 grams in an ounce.
For example, to find out how many grams there are in an ounce and a half, multiply the ounce value by the conversion factor, that makes 1.5 oz * 28.35 = 42.5 grams in 1.5 ounces.
Ounce is an imperial (UK) and US customary mass unit and equals to 28.35 grams in both measurement systems. The abbreviation for ounce is "oz".
Gram is a unit of mass in metric system. There are 1000 grams in a kilogram. The abbreviation is "g".