This report discusses the calculation of x-ray doses in three dimensions using a treatment planning database which was measured in two dimensions only. It concerns the common assumption that wedged field profiles in the non-wedged direction are similar to open-field profiles for the same field size and depth. It shows the extent to which this assumption can lead to errors in wedge dose calculation for both solid and dynamically wedged fields on Varian linear accelerators at 6 MV. Finally it shows that this assumption tends to produce more accurate results when used to calculate doses for dynamically wedged fields and why, even in the wedged direction, some of the simpler treatment planning algorithms are more suitable for dynamic wedges than they are for solid wedges.