Standard weight of a sack of wool for export was 364 lb; the standard calculation was that c.240 sheep were required to produce one sack. Wool was the most important English export of the 13c and 14c. There were some 50 grades of wool at the time; the finest in the 13c came from Tintern Abbey and Abbey Dore in the West Country and from Stanfield in Lincolnshire. A sack of such wool fetched 28 marks (£18) on the Flemish market, while lesser-rated wool would fetch 7-12 marks. In 1335-6 some 34,000 sacks of wool were sent to Flanders and Brabant. [OldEngl. saecc = sackcloth] -
Cf. Sarpler
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.