An exemplary calorimeter includes a body configured to capture radiation generated by a source of the radiation, such as without limitation a laser, and absorb energy from the captured radiation. The calorimeter is simple to manufacture, operate, and maintain and is compact, highly accurate, able to withstand high power beams, and self-calibrating. NIST traceable electrical wires are used for the measurement. No fluids are used during measurements of the input radiation. A simple built in fluid or gaseous cooling system may be used post-measurement to reset the calorimeter temperature back to ambient for repeated measurement capability.