The purpose of the research is to reveal the role of the conventional translation norm and types of translation equivalence in methodology for evaluating translation quality by analysing their mutual influence. The article provides a brief contrastive analysis of translations of the English prose samples in different time periods, which made it possible to trace changes in the conventional norm and identify variable types of equivalence. The study is novel in that it is the first to develop an algorithm for evaluating translation quality by integrating factors that affect the final result of translation activity. As a result of the study, a scale for evaluating translation quality which integrates the main factors that affect it was developed.