The present study employed 600 subjects and extended earlier experiments under 'ideal' conditions to white noise. When known experimental biases were eliminated, half loudness was equal to half sound-pressure level (-6 dB) from 45 through 90 dB. The same simple relation held whether stimulation was through headphones or loudspeaker, and whether responses were numerical estimates or marks on a linear loudness scale. These findings and other evidence support the physical-correlate theory of sensory intensity and suggest that quantitative estimates of sensation are based not on the quantitative nature of sensory events as such but rather on the external events and relations they signify.