The American Fly Fishing Trade Association (AFFTA) provides standardized weights for fly lines, which you can find below. While most anglers simply use the general line weight measure when matching a line to a rod, occasionally more detailed information is useful. The table below provides the official measurements in both grains and grams. This may also be useful when trying to determine what line weight an unmarked line is, as you can simply place it on a precision scale.
Standard Single-Handed Fly Lines
(Weight is for the first 30' of line minus level tip)