Homeowners and researchers frequently estimate the radon concentrations in various areas of the home from a single radon measurement often performed in the home's basement. This study describes the spatial variation of radon concentrations both between floors and between rooms on the same floor. The geometric mean basement and first floor radon concentrations for one-story homes were 13.8% and 9.0% higher, respectively, as compared to their counterparts in two-story homes. The median first floor/basement ratio of radon concentrations for one-story homes was 0.60. The median ratios between first floor/basement and second floor/basement for two-story homes were 0.51 and 0.62, respectively. The mean coefficient of variation for detectors placed on the same floor was 9.5%, which was only 2.6% higher than the mean coefficient of variation found for collocated (duplicate) quality control detectors. The wide individual variations noted in radon concentrations serve as a reminder of the importance of performing multiple radon measurements in various parts of the home when estimating home radon concentrations.