The pound in use in Offa's day, also known as the Saxon pound or moneyers' pound, remained essentially unchanged until 1526, by which time it had come to be known as the Tower pound. In 1526, the Tower pound was replaced by the (English) troy pound, which was, by law, equal to exactly 16/15 of a Tower pound. The Tower pound thus had a mass of 5400 English troy grains, or approximately 349.9 grams. The Tower pound was divided into 12 ounces, each ounce into 20 pennyweights, and each pennyweight into 32 grains. There were thus 640 grains to an ounce, 7680 grains to a pound. These grains were of a type known as the "wheat grain," as opposed to the much larger grain of the troy and avoirdupois systems, sometimes known as the "barleycorn." The Anglo-Saxon (Saxon / moneyer's / Tower) pound remained in use for silver coinage in England until 1344, and for weighing gold and silver until 1526.
^A proclamation of Henry VIII, 5 November 1526. Proclamation 112 in Paul L. Hughes and James F. Larkin, editors. Tudor Royal Proclamations. Volume 1. New Haven: Yale University Press,1964.
^R. D. Connor and A. D. C. Simpson.Weights and Measures in Scotland. A European Perspective.National Museums of Scotland and Tuckwell Press, 2004, page 116, quoting from H. W. Chisholm, Seventh Annual Report of the Warden for the Standards..for 1872-73 (London, 1873), quoting from 1864 House of Commons Paper.