We obtained interferometric observations of 6 spectral type O stars and 25 spectral type B stars with the Precision Astronomical Visible Observations (PAVO) and the CLassic Interferometry with Multiple Baselines (CLIMB) beam combiners at the Center for High Angular Resolution Astronomy (CHARA) Array on Mt. Wilson, California. All luminosity classes were represented with 3 supergiants, 16 giants, and 12 dwarf stars. We directly measured the angular sizes of these stars with an average error of 10% for the O stars and 6% for the B stars. The stars range in size from 1.090 milliarcsec (mas) for beta Tau down to 0.12 mas for 10 Lac, the smallest star yet resolved with the CHARA Array. These observations represent the first interferometric observations of O stars since 1974 (Hanbury Brown et al. 1974). We collected ultraviolet to infrared spectrophotometry for these stars, and we derived angular diameters and reddening estimates that best fit the spectra when the effective temperature was set by published results from analysis of the line spectrum. We find that the model based angular diameters slightly overestimate (by ~ 4%) the observed angular diameters for our O-star and B-star samples. We also present estimates for the effective temperatures of these stars derived by setting the interferometric angular size and fitting the spectrophotometry. We find the spectroscopic based effective temperatures are smaller (~7%) than our interferometrically derived temperatures for all B-stars in our sample. Finally, we place our sample stars on an observational HR-diagram based on our measurements.