It depends greatly on the era we are discussing, and unfortunately I can't speak much on European feudalism. However, I may be able to give some insight into the Japanese model. The currency standard for much of Japan's history was the koku. It was supposed to be the amount of rice it would take to feed a man for one year. A fiefs wealth was measured in this fashion. Additionally, Japan had a caste system. Samurai, the obvious warrior class, were at the very top for the better part of the last millennia. After samurai were farmers. Below the famers were artisans. Merchants, whom were thought to be lesser due to their lack of tangible contribution were almost at the very bottom. As in many caste systems, the bottom was occupied by an "untouchable" class. To this day, these people suffer some degree of discrimination and under representation in politics and high level positions. This caste system is what really started to slay the feudal system in the country. During the two hundred and fifty years or so of relative peace after 1614, the warrior class found themselves out of a job. You can maybe guess that the lowly merchant began to have quite a large degree of practical power in a peaceful economy. The system was clearly unsustainable, especially with encroaching western powers.