Abstract—Measuring Inconsistency in ontologies is an important topic in ontology engineering as it can provide extra information for dealing with inconsistency. Many approaches have been proposed to deal with this issue. However, the main drawback of these algorithms is their high computational complexity. One of the main sources of the high complexity is the intractability of the underlying Description Logics (DLs). In this paper, we focus on an important tractable DL family, DL-Lite. We define an inconsistency degree of a DL-Lite ontology based on a three-valued semantics. We also present an algorithm to compute this inconsistency degree and show that its time-complexity is PTime in the size of ABox and TBox. Keywords-Measuring; Inconsistency Degree; DL-Lite; ontologies;