Insect screens are mounted on the wall and not on the window frame. That's why you need to measure the width and height of your window opening to determine the size of your insect screen accurately.
To calculate the correct size, measure the inner wall width (A) and height (B) where the screen will be installed. Use these measurements to find the appropriate size code for your insect screen. Please note that insect screens are not suitable for VELUX 3in1 and 2in1 roof windows (GGLS & GPLS).