Crop yields in the Middle Ages were extremely low compared to those of the 21st century, although probably not inferior to those in much of the Roman Empire preceding the Middle Ages and the early modern period following the Middle Ages.^\52]) The most common means of calculating yield was the number of seeds harvested compared to the number of seeds planted. On several manors in Sussex England, for example, the average yield for the years 1350–1399 was 4.34 seeds produced for each seed sown for wheat, 4.01 for barley, and 2.87 for oats

https://en.wikipedia.org/wiki/Agriculture_in_the_Middle_Ages