How much window film do I need?
The layout on the roll, not the glass area, decides how much window film you need. Film is sold in rolls of set widths (usually 122, 152 and 183 cm); each pane is cut separately and the strip of roll left beside it often cannot be used. This page opens the tool with solar control film and four 120 × 150 cm windows: the result is 6.6 metres of film from a 152 cm roll.
Method
- Trim allowance: 2.5 cm is added to every edge of every pane. A 120 × 150 cm pane is cut at 125 × 155 cm; the excess is trimmed at the glass edge on site.
- Roll width: If the cut size fits the roll width, the pane comes out in one piece. If rotation is allowed, the pane is also tried turned by 90°.
- Strips: If the pane is wider than the roll both ways, it is split into vertical strips joined with a 0.3 cm overlap, which creates a seam.
- Layout: Pieces are placed on shelves side by side and one after another along the roll; the total shelf length is the layout length.
- Waste allowance: 5% is added to the layout and the length is rounded up to 0.1 metre.
In the example each shelf on the 152 cm roll holds one pane: 4 × 155 cm = 6.2 m, or 6.6 m with the waste allowance. The glass area is 7.2 m² and the film used is 10.0 m²; the difference is the layout offcut at the roll edge and the allowances.
How the roll width changes the result
The same four windows do not fit a 122 cm roll: the 125 cm cut width is wider than the roll, each pane is covered with two strips and the length rises to 13.1 metres. On a 183 cm roll the panes are rotated (the 155 cm side runs across the roll) and the length drops to 5.3 metres. Below the result the tool compares every roll width; it recommends the one without seams first, then the one with the least film area.
On large shop fronts a seam may be unavoidable: three 200 × 250 cm shop windows need 13.4 metres of film from a 152 cm roll, with one vertical seam on each pane. Seams can be seen up close, so choose the widest roll available for shop fronts.
Before installation
Buy film for the panes of one façade from the same lot; batches can differ in tone. Panes over 2 m² are filmed by two people. On double and insulated glazing film can cause thermal stress, so check the manufacturer’s glass compatibility table.
Source: trim allowance and waste method from the docs/13 research (Window Place, Decords); roll widths are approximate and will be confirmed against stock. The result is a preliminary estimate; measure the panes before ordering.
Last updated: 20 October 2026 · Full tool page
