RNA is usually single-stranded, although there may actually be double-stranded forms due to hybridization or higher structure. If your question about dsRNA quantification refers to mass weight (ng or ug), but not molecular molar quantity, I think both double-stranded and single-stranded RNA are the same by using nanodrop to measure. For example, you mix 1 ug of sense ssRNA (a single specific kind of RNA) with 1 ug of the ss-antisense of that RNA, and they are 100% paired to form a dsRNA, you will get 2 ug of RNA. Although it has not changed molecularly in quantity, its mass will still increase.