Determine the width of the curtain:
The required width is always determined by the size of the valance or curtain rail (A), not the width of the window.
If you are installing a new harness, it is advisable to make it about 10-20 cm longer on each side of the window. This way, when the curtain is pulled aside, it will not cover the glass surface. It is recommended to fix the curtain at least 15 cm above the top of the window.
When using rod curtains, the decorative elements at the end of the rod are not included in the width of the curtain.
In the case of curtains, the measurement is taken between the edges of the inner frame of the window, and a few centimetres are added to allow for the curtains to extend beyond the glass.(E)

Calculate the length (height) of the curtain:
The length of the curtain can be defined in several ways: it can reach the windowsill (B), hang slightly below (C) or even the floor (D).
To get an accurate result, measure the height at least at three points (left, middle and right), as the floor, ledge or cornice is not always perfectly straight. The lowest of the three measurements should be taken.
The starting point of the measurement should be the centre of the clips or curtain rings at the top.
If you want the curtain to reach the sill or the floor, subtract 2 cm from the resulting size to avoid the material touching the surface and getting dirty or friction.
If there is no sill or if the cornice is within the plane of the sill, measure the distance to the bottom edge of the window or sill and add about 15-20 cm.
If there is a radiator under the window, make sure that there is at least 2 cm between the curtain and the radiator to allow for proper airflow and safety.