A beam dose computing method includes dividing a surface area of a target object into include first, second and third regions of different sizes, the third regions being less in size than the first and second regions, determining first corrected doses of a charged particle beam for correcting fogging effects in the first regions, determining corrected size values for correcting pattern line width deviations occurring due to loading effects in the second regions to create a map of base doses of the beam in respective of said second regions and to prepare a map of proximity effect correction coefficients in respective of said second regions, using the maps to determine second corrected doses of the beam for proximity effect correction in the third regions, and using the first and second corrected doses to determine an actual beam dose at each position on the surface of said object.