You will first need to measure the glass, in centimetres, using a tape measure. Only measure the glass you want to cover.
Width: measure from left to right at the top and the bottom of the glass, and take note of the largest measurements (some older wooden windows are not perfectly square).
Height: measure from top to bottom on the left and the right of the glass, and take note of the largest measurements.
Leaving a clear gap around frosted or patterned film is a stylish and practical option, allowing you to peep out when someone is at the door for example. To create a clear outline around the film, deduct twice the width of the desired clear outline, to the width and the height of your pane.
For example, if you want a 1cm (10mm) clear gap all the way round, deduct 2cm from the width, and the same from the height.
Fitting the film with a gap all the way round is much easier, especially on old wooden windows and doors which are not always in the best condition, and where the edge of the glass has paint encroachment.