In this study, new single number quantities (SNQs) based on 1/3 octave band sound pressure levels and low-frequency noise criteria were proposed to evaluate low-frequency noise in indoor spaces. The suitability of the proposed SNQs (Dmax and Dsum) was assessed through correlation analysis with other existing SNQs (LCeq and LZeq) and confirmed by an auditory experiment conducted for construction and air-conditioner outdoor unit noise to be infiltrated from outdoor to indoor spaces. The result showed that the proposed SNQs were highly correlated with the existing SNQs in the range of 0.81 to 0.95. The auditory experiment also revealed that the proposed SNQs had a high correlation with subjective annoyance in the range of 0.81 and 0.89 out of the total range of presentation levels, and a similar correlation with existing SNQs for each presentation level. The proposed SNQs will be able to identify the major frequency bands in terms of annoyance and help assess and establish countermeasures at the site of the low-frequency noise.