We make quantitative estimates of the impact of roof reflectivity on cooling and heating energy use for buildings in the US. Prototypical buildings are simulated with reflective (light in color) and absorptive (dark in color) roofs. Differences of annual cooling and heating energy use and peak electricity demand between dark and light roofs yield the savings. The DOE-2 building energy simulation program is used for these calculations. Monetary savings are calculated using local utility rates. Savings are estimated for 11 US metropolitan statistical areas (MSAs) in a variety of climates. The total savings for all 11 MSAs are: annual electricity savings, 2.6 terawatt hours (TWh); net annual savings, $194 M; and peak electricity demand savings. 1.7 gigawatt (GW). Extrapolating the savings from the 11 MSAs to the entire United States, we estimate annual electricity savings of about 10 TWh and a net savings of about $750 M in annual energy payments. Peak electricity power reduction is estimated to be about 7 GW.