customary cup = 16 tablespoons exactly using the old U.S. customary tablespoon of 1 ⁄ 2  U.S. fl oz. ^ exactly ^ by 1891 definition ^ One gram per millilitre is very close to one avoirdupois ounce per fluid ounce: 1 g/mL ≈ 1.002 av oz/imp fl oz This is not a numerical coincidence, but comes from the