Window Film Calculator
Window film is applied to glass to reduce heat gain, block UV rays, add privacy, or improve safety. Ordering the right amount of film avoids having to buy a second roll mid-project. This calculator takes the number of windows you are covering, the average window width and height in inches, and your chosen roll width (typically 24 or 36 inches) to determine the total square footage of film needed and the roll length required. A 10 percent waste allowance is included for trimming, overlap, and installation mistakes. For best results, measure each window individually and add the areas together rather than using averages; this calculator uses averages as a quick estimate. Choose a roll width that is wider than the widest window pane you need to cover to avoid seams within a single pane. If your windows vary significantly in size, group similar-sized windows and calculate each group separately.
Window film formula
Window area (sq in) = Width x Height
Total area (sq ft) = (Window area x Number of windows) / 144
Area with waste = Total area x (1 + Waste %)
Roll length (ft) = Area with waste / (Roll width (in) / 12)
Worked example
6 windows, 36 in wide x 48 in high. 36 in roll width. 10% waste.
- Window area = 36 x 48 = 1,728 sq in = 12.00 sq ft
- Total = 12.00 x 6 = 72.00 sq ft
- With 10% waste = 72 x 1.10 = 79.20 sq ft
- Roll width in feet = 36 / 12 = 3 ft
- Roll length = 79.20 / 3 = 26.40 ft
Frequently asked questions
How do I calculate how much window film I need?
Multiply the width by the height of each window in square inches, convert to square feet, and add up all windows. Add 10 percent for overlap, trimming waste, and mistakes. Then divide the total area by your roll width (in feet) to get the roll length needed.
What roll widths does window film come in?
Window film is most commonly sold in rolls 24 inches (2 ft) or 36 inches (3 ft) wide for residential use. Some commercial grades come in 48 inch or 60 inch widths. Choose a roll width that is wider than your widest window to minimize seams.
Can window film be applied to any glass?
Most window films can be applied to standard single-pane, double-pane, and tempered glass. Some low-emissivity (Low-E) coated glass and some laminated glass may not be compatible with all film types. Check the film manufacturer's specifications and consult a professional for unusual glass types.
How long does window film last?
Quality residential window film typically lasts 10 to 15 years when professionally installed. DIY installations may have shorter lifespans if bubbles or edge lifting occur. UV-blocking films degrade gradually over time and may need replacement to maintain their UV rejection properties.
Does window film reduce heat and UV?
Yes. Solar control window films can reject 40 to 80 percent of solar heat, depending on the film type. Most quality films also block 99 percent of UV rays, which helps protect furnishings and flooring from fading. Performance varies by film type and solar orientation of the window.
Sources
- International Window Film Association (IWFA): Window film standards and guidance.
- US Department of Energy: Window Films.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. Measure each window individually for a precise order.