Window film adds privacy, cuts glare and heat, blocks most ultraviolet light or simply decorates a pane. It is sold in rolls of a fixed width, and each pane is cut from strips that run its full height. This calculator works out the length of film and the number of rolls for a set of windows.
How the calculation works
- Strips per pane = pane width ÷ roll width, rounded up
- Length per pane = strips × (pane height + trimming margin)
- Total length = number of panes × length per pane
- Rolls = total length ÷ roll length, rounded up
Measure only the visible glass, inside the frame or the gaskets, and add a margin of 1 to 2 in per cut: film is applied slightly oversize and trimmed in place.
Example
Six panes of 36 × 48 in with a 36 in roll need one strip each, cut 50 in long. That is 300 in, or 25 ft of film, so 2 rolls of 36 in × 15 ft. The glass covers 72 sq ft.
Fewer offcuts
- Choose a roll width close to the width of your panes: a 36 in pane cut from a 48 in roll wastes a quarter of the film.
- Two narrow panes can sometimes be cut side by side from a wide roll.
- Seams are visible: when a pane is wider than the roll, butt the edges carefully, or turn the film sideways if the pane is shorter than the roll is wide.
Types of film
| Film | What it does |
|---|---|
| Frosted or decorative | privacy while letting light in |
| Mirror (one-way in daylight) | privacy from outside during the day only |
| Solar or heat control | rejects part of the solar heat and cuts glare |
| Low-E | keeps heat inside in winter |
| Security | holds broken glass together |
Most films block about 99% of ultraviolet light, which slows the fading of floors and furniture.
Applying film
- Clean the glass thoroughly, scraping off paint and dirt with a razor blade.
- Spray the glass generously with water and a drop of baby shampoo.
- Peel the liner, spraying the adhesive side as you go, and lay the film on the wet glass.
- Squeegee from the center outward, then trim the edges with a sharp knife and a straightedge, leaving a 1/16 in gap.
Check with the window manufacturer before applying heat-control film to insulated or low-E double glazing, as it can affect the warranty and, on dark films, increase the risk of thermal stress cracks.