This paper presents key findings about on-screen optimal line length for tablet personal computers (PCs). It examines the effects of four different line lengths on the reading speed and reading efficiency. Seventy participants ranging between the ages of 20 and 40 participated in this study. They read four different texts with an average length of 2000 characters. The texts contained substitution words, which were to be detected by the subjects to measure reading accuracy. Moreover, the subjects were asked to subjectively vote on their reading experience in the context of subjective measures like reading speed and accuracy. The results of the study revealed that 90 characters per line (CPL) were preferred by most of the participants. Nonetheless, some participants falling between the ages of 35 and 40 years preferred 60 CPL. The findings presented in this paper are quite worthwhile as the Tablet PC are extensively used for e-reading. In essence, this study suggests optimal line length for reading on screen using Tablet PC and eventually benefiting people who use Tablet PC for reading, hailing from every walk of life.