This paper explores English learners' ability to guess the meaning of unknown words from their linguistic context. Specifically, the study focuses on (1) the optimal ratio of unknown to known words in which Japanese EFL learners can guess successfully and (2) the relationship between different contextual clues and their use by about 300 Japanese high school students in different grades; i.e., first- to third-years. Findings show that there is no significant difference between the means in success rates for the two groups for either ratio: 1:35 or 1:40. This is regardless of participants' grades although more students can guess successfully in a ratio of 1:40 than in the 1:35 ratio. There is only one exception where there is a significant difference between the two groups of first-year students regarding one passage. Moreover, the results indicate that there is a significant difference in the use of contextual clues though there is one exceptional case for first-year students. The results also show that there is a significant difference between the use of local and global clues.
