The standard height of our pelmets is approximately 23 cm they vary slightly depending on the mouldings used at the top, but that is just our standard size, they can be made to what ever height is needed. Like the corner piece shown here, this was a sample made to show a customer how a heavier moulding top and bottom was needed to keep the proportions correct to take the overall height of the pelmet to 38 cm. The height of the pelmet was needed as the windows they were wanted for were in period property and very high, the standard pelmets would have looked lost way up at the top.
It depends on what is going to be hung at the windows as to how deep the returns need to be i.e. blinds, curtains e. t. c. For most curtains 15 cm works well, for blinds depending on how they are fastened, the returns can go down to 7-9 cm, but these are only guide lines and the pelmets can be made exactly to suit the individual circumstances they are required for.