The aim was to determine the optimum number of ambient exposure fractions required in the human exposure model for accurate computation of annual erythema effective solar exposure. Methods: Ambient exposure fractions were determined on a daily basis over a period of a year in the Rockhampton region using ambient exposure measurements and erythema effective solar exposure measurements at selected body sites of Australia post mail delivery personnel (APMDP). Several values of annual erythema effective exposure for the same body sites were computed using different combinations of ambient exposure fractions on a monthly, seasonally and half-yearly basis in the human exposure model and compared with the measured values. Results: This method enabled a check on the accuracy of annual erythema effective solar exposure estimation using the different combinations of ambient exposure fractions in the human exposure model. In the worst case there was approximately 35% difference between the measured value and the computed value. Conclusion: The best accuracy was obtained with the use of ambient exposure fractions on a monthly basis where most of the estimated values for the different body sites were within 20% of the measured values.