The purpose of this study is to develop Text Complexity Formula more precisely. For this, we focused on complementing the list of words and elaborating the measurement of Sentence Complexity. Independent variables used in this Formula are graded vocabulary list and the figure of sentence complexity calculated by the length and structure of sentence. The dependent variable is the determination on text of the appropriate grade level by experts using regression analysis. We suggested two Text Complexity Formulars through multiple regression which has the power of explanation of 75.2% about difficulties of texts in elementary level and 65.6% in middle school level. The Text Complexity Formula, we finally determined, is as follows. ETGL = 0.032uWa - 0.391S + 0.016uWaS + 7.438* R2 = 0.752ETGL = Elementary Text Grade Level uWa = The number of words except word list A S = The number of sentence uWaS = The number of words except word list A × The number of sentence STGL = - 0.060Wa + 0.145uWc + 0.110C + 0.024uWcC + 9.075* R2 = 0.752STGL = Secondary Text Grade Level Wa = The number of words in word list A uWc = The number of words except word list C C = Degree of Sentence Complexity uWcC = The number of words except word list C × Degree of Sentence ComplexityThis Text Complexity is only focused on the quantitative features of the internal texts. So, it is necessary to conduct follow-up studies for supplementing the formula through including the qualitative factors of the text like Reader variables(reader’s background knowledge) and Task variable.