This paper is a survey and a progress report on present and potential instrumentation to measure loudness levels of sounds. The development of the sound‐level meter (SLM) in the 1930's, its technological and psychoacoustical evolution, and its evaluation as a measurement device are discussed. A loudness‐level monitor, designed to measure the relative loudness level of broadcast programs directly on an indicating instrument, and the development of a new set of equal‐loudness contours are described, together with a new law of loudness‐level addition for combined bands of noise which was discovered during the research. An experimental loudness level meter, devised by adapting CBS Laboratories' loudness level monitor and the potential development of an accurate and practical loudness‐level indicating device are discussed. The results of psychoacoustic evaluations of the loudness level meter versus sound‐level meter are given.