Touch devices are widely integrated into various environments, including corporate settings and public information kiosks. The size of touch screen interface buttons significantly affects user interaction efficiency and accuracy. Current research predominantly focuses on button sizes for handheld and desktop devices, leaving a gap in studies on large touchscreen displays. To address this gap and improve user experience and operational efficiency, this study investigates nine button sizes on a 65-inch touchscreen tilted at a 90-degree angle to evaluate operational performance across different button sizes and spacing intervals. Twelve participants, stratified into two age groups (55 + and 25–55), completed tasks involving sequential button selection. Nine button sizes (10 mm to 50 mm) and four spacing intervals (25 to 100 pixels) were tested. Results showed a negative correlation between button size and response time for both age groups, with larger buttons yielding shorter response times. The optimal button size was 30 mm for younger participants and 40 mm for older participants. Accuracy rates were high (>97%) across all button sizes, with larger buttons enhancing accuracy. These findings underscore the importance of age-specific design considerations in multi-touch interfaces to optimize usability for diverse user demographics.