Millimeter-wave links, which will be applied in 5G wireless communication, can suffer severe attenuation and multipath fading in indoor channels. Accurate indoor channel modeling for path loss is hence important. In this paper we address this for frequencies of 5, 31 and 90 GHz. An indoor environment is modeled and simulated via the X3D ray-tracing method in Wireless Insite® software, and results are post-processed in MATLAB. Measurements at each frequency were also made in the indoor environments for link distances up to 50 m. Two types of widely-used log-distance path loss models are used for comparing results: the close-in (CI) free-space reference model and the floating intercept (FI) model. Path loss simulation results are compared with measurement for different frequencies, antennas, and channel conditions. Our results show that CI model slopes between ray-tracing and measurements differ by less than 0.3, and model standard deviations differ by less than 2 dB for all frequencies for the line of sight (LOS) case. For a non-light-of-sight (NLOS) channel, differences are less than 0.6 for slope and 5 dB for standard deviations, illustrating the utility of ray-tracing for these frequencies and settings.