The sextarium was a measure of unknown and probably variable quantity since there are references in Domesday to both royal and local standards, to dry and liquid measures, and to large and small sesters. Early in the next century, Henry of Huntingdon equated the Anglo-Saxon sester with a horse-load (Historian Anglorum, edited by Diana Greenway (1996), pages 374-75).
The sester was the most common measure of volume in Domesday Book, used for quantities of barley, flour, honey, oats, rye, salt, wheat and wine. It may normally have represented about 2 pints in liquid volume, and 16 bushels as a dry measure, as often in later times.
For more detail, see Philip Grierson, 'Weights and measures', Domesday Book: studies, edited by Ann Williams and R.W.H. Erskine (1987), pages 80-85.