The globally averaged solar insolation is given by the ratio of the total sunlight absorbed by the Earth to the area of the Earth. If F_s is the intensity of sunlight reaching the Earth (normal to the path of sunlight), and the total cross section of the Earth is PI*R²
The amount of sunlight absorbed by the Earth is F_s*(1-albedo).

The total area of the Earth is 4*PI*R².

So this gives the global average solar insolation as F_s*(1-albedo)*PI*R² / [4*PI*R²]
                =Fs*(1-albedo)/4
This is balanced by outgoing longwave radiation (sigmaT⁴) and an effective temperature of the planet can be found
                T_e=[ F_s*(1-alpha)/(4*sigma)]^1/4
(where sigma is the Stefan-Boltzmann constant)
Results from this model compare favorably for many of the solar system's planets.