Text readability plays a crucial role in measuring the ability of the learner or the reader. In particular, content designers of reading materials for teaching and practical purposes should concentrate on writing texts based on the target readers’ levels in a national context. If text readability is not understood, it is like using drug that is incompatible with the disease. This research aims to create a formula of grade levels for text readability in Khmer by selecting all Khmer texts on the Let’s Read! website (developed by The Asia Foundation) and analyzing them using Multiple Linear Regression. As a result, researchers can draw the Multiple Linear Regression of Y = b₀ + b₁X₁ + b₂X₂ + b₃X₃ with a constant value of b₀= -3.587; the value of b₁ = 0.397; the value of X₂ = the average sentence length (total number of words divided by the sentence); the value of b₂ =1.234; the value of X₂ = the average number of syllables per word (total number of syllables divided by the total words); the value of b₃ =0.444; the value of X₃ = the percentage of high-frequency words per text (total number of high-frequency words divided by the total words); and the coefficient of determination of Model Summary of R Square (R²) = 0.958, F (3, 417) = 3167.092, p < .001; and adjusted R² = 0.958. A formula of grade levels for text readability in Khmer was developed as Grade Level (Y) = -3.587 + 0.397 (average sentence length) + 1.234 (average number of syllables per word) + 0.444 (the percentage of high-frequency words per text). Based on the results, curriculum designers, writers, and other stakeholders can consider preparing reading texts according to the grade level formula to meet the needs of learners and readers.