Measurement of solar radiation is not often feasible except at instrumented research facilities. Although estimates of direct beam solar radiation in the absence of an atmosphere or with cloudless skies may be obtained from theoretical equations or tables, they are unrealistic to the extent that they fail to consider scattered solar radiation and are unapplicable whenever clouds are present. This paper presents a simple model for estimating daily total solar radiation by modifying existing theoretical equations to take into account scattered radiation from clear skies and reflected and transmitted radiation from clouds. Observational data required are: station latitude, slope direction and inclination, and estimated mean hourly cloud cover, by month. Tests of estimated daily total solar radiation by months against comparable measured radiation for several areas in the Pacific Northwest indicate that the model yields estimates that reproduce measured daily totals with a high degree of accuracy. Results were similar when the model was used to estimate solar radiation in the northeastern United States. Forest Sci. 24:363-373.