Evaluating Soft Keyboard Parameters for Tablet Productivity: Usability-Centric Layouts

The increasing diversity in tablet form factors and their use in productivity scenarios presents considerable complexity in soft keyboard design, necessitating updated guidelines for layout parameters to ensure usability across varying screen orientations. This study investigates how two core soft keyboard layout parameters, key size and key aspect ratio, influence user input performance and subjective experience on tablets across different screen sizes and orientations (portrait vs. landscape) in productivity-focused multilingual typing tasks. Two within-subjects experiments (N=20) were conducted using a portrait-mode Surface Pro 9 and a landscape-mode ASUS ZenBook 17-Fold OLED, testing five levels of key sizes (8-14mm portrait; 15-20mm landscape) and five levels of key aspect ratios (0.6:1-1:1 portrait; 1:1-1.4:1 landscape) respectively, collecting both objective performance data (WPM, TER) and subjective ratings (5 dimensions). Results indicate that while objective performance measures showed no significant differences for the tested parameters, subjective ratings strongly favored specific configurations: approximately 12mm keys in portrait mode and 17mm keys in landscape mode were preferred for key size, and aspect ratios of 0.9:1 (portrait) and 1.1:1 (landscape) were most favored, primarily driven by perceived comfort and usability. These findings underscore the critical role of context-dependency and subjective user experience in soft keyboard layout optimization for tablets, providing concrete, data-driven recommendations for designing more usable and contextually appropriate interfaces for productivity tasks.