Scientists at the National Institute of Science and Technology (NIST) have constructed a laser power and energy measurement system based on a cryogenic radiometer. Since the 1960s, the institute has built and maintained electrically calibrated calorimeters to calibrate laser power and energy detectors. The current generation of calorimeters has an uncertainty standard of 0.25 percent because they operate at room temperature. The new system is based on an electrically calibrated cryogenic radiometer operating near liquid helium temperatures. The uncertainty standard is gauged at 0.02 percent or less.