Design temperatures, used widely in the heating and air-conditioning industry, are calculated from hourly temperature data. However, there are relatively few locations with long-term records of hourly temperatures, limiting the number of locations for which design temperatures can be calculated. To address this limitation, techniques were developed to estimate winter and summer design temperatures using widely available daily minimum and maximum temperatures. For two of the techniques, mathematical functions (exponential and power law) were fit to the cumulative distribution functions (CDFs) for daily temperatures and for hourly temperatures. General transformations were developed to relate the parameters of the daily CDF functions to the parameters of the hourly CDF functions. For the third technique, the hourly CDF was synthesized empirically from the daily temperatures. All three techniques produced good estimates. Best results for winter design temperatures were obtained using the empirical synthesis technique. Best results for summer design temperatures were obtained using the power law function, but the results using the exponential function were almost as good. The large number of stations used in this study, representing all areas of the U.S., provide confidence in the application of these techniques across a wide range of climates.