Objectives: To quantify the energy expenditure of Australian Football training and matches and the total daily energy expenditure of Australian Football players using tri-axial accelerometers.Design: Cross sectional observation study.Methods: An algorithm was developed for the MiniMax 4.0 (Catapult Innovations, Scoresby Australia) using measured oxygen uptake and accelerometer data to estimate energy expenditure of 18 Australian Football players during training and matches. The algorithm was used to validate a metabolic power calculation used by Catapult Innovations (Scoresby Australia) in their proprietary GPS software. The SenseWear™ (Model MF-SW, Bodymedia, Pittsburgh, PA) armband was used to determine non-exercise activity thermogenesis and was worn for 7 days leading into a match. Training, match and non-exercise activity thermogenesis data was summed for total daily energy expenditure.Results: Energy expenditure for field training was estimated to be 2719 ± 666 kJ and for matches to be 5745 ± 1468 kJ. The estimated energy expenditure in the current study showed a large correlation (r = 0.57, 90% CI 0.06–0.84) with the metabolic power calculation. The mean total daily energy expenditure for an in-season main training day was approximately 18,504 kJ and match day approximately 19,160 kJ with non-exercise activity thermogenesis contributing approximately 85% and 69% on training and match days, respectively. Conclusions: The MiniMax 4.0 and SenseWear™ armband accelerometers provide a practical, non-invasive and an effective method to successfully measure training and match energy expenditure, and non-exercise activity thermogenesis in field sport athletes. Taking methodological limitations into consideration, measuring energy expenditure allows for individualised nutrition programming to enhance performance and achieve body composition goals.