20 inch (508mm) - generally this is used for most side windows of cars & wagons. Simply use a tape measure and measure from the lower corner of front side window to the lower corner of rear side window, then multiply by 2 for sufficient film for both sides of car. The rear door 1/4 light window is usually cut from the front door off-cut.

60 inch (1524mm) - generally used for rear screens, and other windows that don't cut out of the smaller roll. Measure window across the bottom from corner to corner; on hatchbacks measure across the widest point (usually the centre). This measurement will be the length cut from the 60" roll width, as the film is best fitted 'roll length' across the rear screen (especially if you need to heat shrink any areas). It will also usually supply enough film for a strip at the top of the front windscreen (if allowed).