A comparison between two global solar radiation- and two net longwave radiation flux formulas applied to the calculation of the net radiation flux was made. The differences between the two global solar radiation formulas were fairly small but the ratio of the two net longwave radiation formulas varied from approximately 1.21 under cloudless conditions to 0.25 under completely overcast conditions. The calculation of the net radiation flux was primarily influenced by the calculation of the global solar radiation flux under cloudless conditions, but under overcast conditions it was largely influenced by the calculation of the net longwave radiation flux. The net radiation flux could be predicted successfully only when locally determined constants were used in the equation to calculate the global solar radiation flux and when a cloud adjustment factor was included in the net longwave radiation formulas. Evidence from the literature also indicated that, at least in humid climates, a cloud correction factor is required for the successful calculation of the net longwave radiation flux.