Weight of 18k white gold ring without a scale?

When determining the weight of an 18k white gold engagement ring are the diamonds which are on it INCLUDED in this gram weight? And if not, how does one determine the weight of the diamonds to subtract it from the weight of of the gold? My ring is 18k WG with about a 1/3 carat round cut centered diamond with 20 additional, smaller round cut diamonds surrounding it in the pattern of a flower... it's a size 6.5. Also, I have already figured the price per gram using a conversion from the troy ounce. If I left anything out that might help to determine this please let me know!