A SI-traceable Rydberg atom radiofrequency power meter determines power of reference radiofrequency radiation and includes: a reference radiofrequency source that provides reference radiofrequency radiation; a vapor cell including: a pair of parallel-plate waveguides; a vapor cell wall including parallel opposing faces of the parallel-plate waveguides; and the vapor space physically bounded by the vapor cell wall to contain gas atoms in an optical overlap volume; and a transmission detector that receives the output light from the vapor cell and produces a transmission signal from the transmission detector for determination of power of the reference radiofrequency radiation, wherein the SI-traceable Rydberg atom radiofrequency power meter determines power of the reference radiofrequency radiation by electromagnetically induced transparency of the gas atoms in a Rydberg electronic state, the determination of power being traceable to the International System of Units (SI).