With the prevalent use of visual interfaces and the increasing demand to display more information, information complexity becomes a major concern for designers. Complex interfaces affect the system effectiveness, efficiency, and even safety. Researchers at the Federal Aviation Administration have developed two sets of psychometric questionnaires to evaluate information complexity of air traffic control displays. This study adapted the questionnaires for commercial visual interfaces and validated them with directed and exploratory tasks on three travel websites. The results confirmed that both complexity questionnaires have satisfactory reliability, validity, and sensitivity. But questionnaire B demonstrated higher sensitivity than Questionnaire A.