The Assize of Bread, a complicated system of regulated English bread prices, begun by Henry III in the 13th c., lasted into the 19th, by which time the drawbacks of the system were becoming increasingly apparent.
In 1812-13, Parliament looked into the issue, calling a series of bakers and millers as witnesses. Their inquiry tells us a lot about breadmaking at the time, when the technology was much closer to medieval than the industrialized processes of today.
According to the witnesses:
A bushel of wheat weighed about 58 lbs. but could be a bit more or less depending on the dryness of the year.
A bushel of wheat yielded about 35-47 lbs of flour suitable for making bread, depending on the fineness desired, with about a pound and a half lost in the grinding. A bushel yielded 35-37 lbs of fine white flour, 38-43 lbs of flour suitable for less fine standard wheaten bread, or 43-47 lbs of flour for household bread. The process also produced 16-10 lbs of bran for animal feed, with the finest flour leaving the most bran. The remainder, if any, was coarser flour called thirds or middlings. Unmixed, this could be used for sizing, fed to hogs, or used to make very inferior bread. Mixed with better flour, it was used to make ship's biscuits and bread for the poor.
A 280 pound sack of flour yielded 347 lbs of bread after baking into quatern loaves, or 1.24 pounds of bread per pound of flour. A baker added water, yeast and salt, and not all of the water was lost in baking. Smaller loaves produced less bread per pound of flour because they lost more weight in baking.
Woolgar's The Great Household in Late medieval England calculates that at the not uncommon medieval household rate of 35 loaves a bushel, a bushel would provide .98 lbs of flour per loaf and .79 lbs after baking.
The amount of flour produced per bushel seems low: would the entire household consume loaves that were premium products by early 19th c. standards? And the ratio of flour weight to baked weight seems to be backwards. If early 19th c. bakers could get more than a pound of bread from a pound of flour, why should we think that their ancestors did much worse?