This study seeks to investigate the relationship between text formality and writing quality by quantifying text formality in EFL English writing. In order to conduct the research, 548 English argumentation compositions were evaluated in terms of the five Coh-Metrix text formality dimensions: narrativity, syntactic simplicity, word concreteness, referential coherence, and deep cohesion. Based on the study, there is only a weak relationship between text formality and writing quality, and some facets of text formality, such as narrativity, word concreteness, syntactic simplicity, and deep cohesion, have varying degrees of influence on writing quality and, consequently, on English writing scores. As per statistics, narrativity has a detrimental effect on writing quality; word concreteness has a significant positive correlation with writing quality; syntactic simplicity shows a relatively small negative correlation with writing quality; deep cohesion has a modestly negative correlation with writing quality; and referential coherence has no correlation with writing quality. It is intended that the findings of this study will have some bearing on how English argumentative writing is taught and learned.