In feudal Anglo-Norman England and Ireland, a knight's fee was a measure of a unit of land deemed sufficient from which a knight could derive not only sustenance for himself and his esquires, but also the means to furnish himself and his equipage with horses and armour to fight for his overlord in battle. It was effectively the size of a fee (or "fief" which word is synonymous with "fee") sufficient to support one knight for one year in the performance of his feudal duties of knight-service. A knight's fee cannot be stated as a standard number of acres as the required acreage to produce a given crop or revenue would vary depending on, amongst other factors, its location, richness of soil and climate.
Creation of Knight's fees
A knight's fee could be created by a magnate or by the king himself by separating off an area of land from his own demesne, or land held in-hand, which process was known as subinfeudation, and establishing therein a new manor for the use of a knight who would become its tenant by paying homage to his new overlord. This homage was a vow of loyalty to provide knight-service, generally to a maximum of 40 days per annum, signifying that he would have to fight for his overlord in battle. No cash rent was payable. A knight was required to maintain the dignity of knighthood, which meant that he should be well-turned out, with the required number of esquires to serve him in battle, and with horses, arms and armour for all.
Used as a unit for tax assessment
A feudal magnate was assessed for certain feudal aids according as to how many knight's fees he was overlord to. Where a knight's fee was inherited by joint heiresses, the fee would be split into 2 separate manors, each deemed 1/2 a knight's fee, and so-on down to smaller fractions. Thus a magnate could be overlord to, say, 12½ knight's fees.
A knight's fee was not only originally created by the process of subinfeudation, but could itself be split into smaller units by the same process, otherwise than through inheritance. By this means, until the practice was outlawed, a knight could create his own feudal retainer who would pledge fealty to him rather than to the overlord. Such a holding was termed a sub-fee.
It can thus be seen that the knight's fee was the base unit of land valuation for use in the feudal system.
- Feudalism (examples) for a historic example of knight's fees.