Software metrics are widely used to measure software complexity and assure software quality. However, research in the field of software complexity measurement of a class hierarchy has not yet been carefully studied. The authors introduce a novel factor called unit repeated inheritance (URI) and an important method called the inheritance level technique (ILT) to realize and measure the object-oriented software complexity of a class hierarchy. The approach is based on the graph-theoretical model for measuring the hierarchical complexity in inheritance relations. The proposed metrics extraction shows that inheritance is closely related to the object-oriented software measurement and reveals that overuse of the repeated (multiple) inheritance will increase software complexity and be prone to implicit software errors.