Cognitive load theory describes learning in terms of a processing system when all too often working memory is overloaded and learning is impeded. Measuring cognitive load is an important component of research in the area of information processing. The design, delivery, and administration of an instrument, as well as its reliability and validity are discussed as a solution to the measurement of cognitive load. A nine-point subjective rating scale ranging from very, very low (1) to very, very high (9) measures cognitive load, defined as the mental effort needed to complete a task. It is a replica of the instrument used by Paas (1992) and Paas and van Merriënboer (1994). The measurement instrument can be used both on paper and on the Web.