Knowledge is related to the information considered in a particularly useful context under consideration. A knowledge measure as a dual of fuzzy entropy quantifies the knowledge associated with a fuzzy set. In this paper, a new entropy-based fuzzy knowledge measure is proposed and validated. The performance of the proposed knowledge measure is explained using two numerical examples. Furthermore, a new multi-criteria decision-making method based on the proposed knowledge measure is introduced and illustrated using a numerical example. Besides this, four new measures namely a fuzzy accuracy measure, a knowledge measure using fuzzy accuracy measure, a similarity measure, and a fuzzy information measure are derived from the proposed knowledge measure and validated.