[en] Occupants of dwellings are exposed to high concentrations of airborne radon and its daughters and hence it is important to assess the dose received by them. This report describes the various parameters that are used to calculate the dose to the lung. The calculations are carried out by a simple computer model with the help of which one can get the activity to dose conversion factor in terms of either rad or grey per working level month. Typical calculations have been carried out to show that the conversion factor can vary by a factor of 5 depending on some typical input parameters. (author)