In discussions about down garments, people often mention the fill weight and the total weight but the actual values of this ratio (or fill volume/total weight) are not often used explicitly for garment comparisons. Values for clo/oz. are obviously preferable, but they aren't always available. For someone that is principally interested in warmth per unit weight (a person for whom water resistance, tear resistance, zipper configuration, etc. are secondary considerations), the fill weight/total weight ratio, or the fill volume/total weight = (fill weight*fill power)/total weight ratio seems like a useful way to give initial rankings to available products before considering other factors.
In considering down vests, for example, one might quickly assemble this ranking:
For the Nunatak Skaha vest, one gets about 600 cubic inches of theoretical loft per ounce of garment weight. This vest is about 70% down by weight.
There are several obvious caveats. This is not an indication of warmth per unit weight. Fabric properties and construction details make an enormous difference to the real insulative value of the garment. Also, the Skaha vest is certainly too warm for some seasons in some areas, and the cost is about twice that of some of the other vests on the list.
I'm just suggesting that the values of fill weight/total weight and fill volume/total weight seem little used, and might be handy tools for evaluating down jackets, vests, or pants when clo is not available.