Answer:
There are approximately 28.35 gm (grams) of the metric system in one oz (ounce) of the British Imperial and US Standards for weights and measures.
Another answer:
1 avoirdupois ounce = 28.35 gm
1 troy ounce = 31.10 gm (Troy ounces are used for weighing gold, and other precious metals.)
1 fluid ounce = 29.57 ml
1 fl. oz. = 28.34952 grams