In order to examine the method of estimating loudness on general noises in living en-vironments, two steps of subjective experiments were performed using artificial sounds. The results of Experiment 1 suggested that arithmetic average of sound pressure levels in octave bands is an appropriate loudness index for various kinds of sound with broad band spectra as well as the precise index such as the Loudness Level proposed by Zwicker. In order to further examine this fact, Experiment 2 was conducted using test sounds with discrete prominent spectral components. As a result, it has been clarified that the arithmetic average can no longer be applicable to such kinds of sound. In addition to these experimental studies, the relationships among representative noise indices were examined by numerical investigation on various sounds general in living environments. As a result, it has been confirmed that the arithmetic average of SPLs in octave bands from 125 Hz to 4kHz is highly correlated to Loudness Level by Zwicker for general sounds without tonal components.