The Five-Finger Rule is a widely recommended strategy for selecting appropriate reading materials in Extensive Reading (ER) programs, particularly for language learners using graded readers. This study investigates how Thai university students apply and perceive the rule, and how they implement it, using an online survey to collect data from 64 students participating in an ER program. Data on the number of books they assessed, the number of difficult words they encountered, and their reasons for choosing a particular book were gathered. The findings revealed that most students (53.8%) selected books that fell within the recommended difficulty range, aligning with their goal of a moderate challenge that still allows for comprehension. Interestingly, 13.8% of students intentionally chose books at a higher difficulty level, motivated by a desire to expand their vocabulary. These findings suggest that students adapt the Five-Finger Rule based on personal reading goals and language learning strategies.