The measurement consists to check the width and height of the covered window space. You must add to the measured width ( as you like) about 5-10cm and to the height- at least 10cm. Please make attention that a mat, which is 160 cm high, has got about 18 cm after rolling.
In case of an intention to install the mat directly on the window slash, it is necessary to check the width and height of the windowpane and then, add about 3-5 cm to the width and about 6-10 cm to the height.