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Under certain conditions, radar is able to penetrate loose sand to reveal subsurface geology in and areas. However, backscatter from the subsurface is modified by signal attenuation by the sand. To quantify the amount of radar attenuation, a laboratory experiment was conducted to measure radar transmission as a function of radar frequency and sand moisture. The frequency range covers P- through X-bands (0.5-12.6 GHz), and the moisture contents of the sand were 0.3, 4.7, and 10.7% by volume. Results show that addition of the sand causes a small decrease in transmission at low frequencies for all three moisture levels, but the sand causes a larger decrease in transmission at higher frequencies. The transmission measurements were also used to calculate values for attenuation. The dry sand resulted in attenuations of less than 6 dB/m over the entire frequency range. Sand with moisture contents of 4.7 and 10.7% volume caused by attenuations greater than 150 dB/m at the highest frequencies, but the attenuation values calculated for P- and L-band frequencies were less than 10 dB/m even at these relatively high moisture levels. These results challenge previous restrictions that sand must be extremely dry for radar penetration to occur.