Influence of size and location of buttons on the usability of interface on large touch screens

This study examined how large touchscreen buttons affect user task completion time, error rate, and subjective satisfaction (ease of pointing and clicking on targets). In this experiment, 31 participants completed button click tasks of square targets placed at 30 (5 × 6) different locations, with seven button sizes (10 mm, 30 mm, 50 mm, 70 mm, 90 mm, 110 mm, and 130 mm). Repeated measures ANOVAs showed that on a 65'' large touch screen (W 1428 × H 803 mm), 70 mm buttons achieved essentially the best performance in completion time, 50 mm in error rates, and 90 mm in subjective satisfaction, respectively. We also compare the differences in efficiency among different button areas and button sizes. The surrounding area and lower area require a bigger button size to achieve the best performance in terms of error rates and subjective satisfaction. The right area requires a bigger optimal button size than the left area considering error rates, while it is the opposite for subjective satisfaction.Practitioner summary: This study investigates how the size and location of buttons on the increasingly popular large touch screen affect user experience. The study reveals that 70, 50, 90 mm size buttons are recommended when speed, accuracy and satisfaction are priorities respectively. The interaction between button size and button area is significantly different. The surrounding area and lower area require a bigger button size to achieve the best performance in terms of error rate and subjective satisfaction. Considering error rates, the right area requires a bigger optimal button size than the left area, while it is opposite for subjective satisfaction. These findings could facilitate the optimal design of usable large touch screens.