Subjects made magnitude estimations of the loudness of pure tones (100, 400, and 1000 Hz), which were presented at equal and unequal sound pressure levels to the two ears. The results were consistent with a model of linear binaural loudness summation: The estimates of loudness approximated the linear sum of the loudness estimates of the individual left-ear and right-ear components. The relation between loudness and sound pressure, over moderate SPLs, can be described by a power function with an exponent of about 0.6 at 400 and 1000 Hz, 0.75 at 100 Hz.