Abstract
This study investigated the effect of character size on the legibility of sentences, using reading materials with several font sizes (from 4 to 10.5 point of Microsoft Mincho). Participants evaluated the legibility of the materials (Japanese sentences) with a questionnaire containing 13 items, and the legibility was estimated by applying the Item Response Theory to the questionnaire data. The legibility increased approximately in linear with the font size : Reading materials with font sizes of 4 and 6 were evaluated as less legible, those with font size of 10.5 were evaluated as more legible, and those with a font size of 8 were evaluated as “neutral”. Visual acuity of participants influenced the legibility evaluation, though the effect was small.
