Energy intake is a function of energy requirement as determined by resting energy expenditure and activity-induced energy expenditure. Resting energy expenditure can be measured or predicted with an equation based on weight, height, age, and gender of the subject. Activity-induced energy expenditure (AEE) can be estimated with an accelerometer for movement registration. The validity of these measures for estimating energy intake is presented with respirometry assessed resting energy expenditure and doubly-labeled water assessed total energy expenditure as a reference. Prediction of resting energy expenditure based on subject sex, weight, height, and age with equations is applicable for most subjects. For some ethnicities or for subjects with an exceptional physical activity level like athletes, measurement of body composition is indicated; to use a fat-free mass-based equation. For activity-induced energy expenditure, a valid sensor for body movement should allow explaining most of the variation as observed with the reference; doubly-labeled water assessed total energy expenditure.