Calorimetry is the most direct, absolute technique for absorbed dose measurements. To improve the measurement accuracy for use with quantitative radiography, a calorimeter has been developed for LANL’s pulsed radiographic machines which produce bremsstrahlung radiation fields of 50–200 Rad per pulse at 1 meter from the source. This paper describes the theory of operation, the calorimeter design, and presents results from the PHERMEX accelerator.