Window area & square-footage calculator
Convert a window’s width and height in inches to its glass area in square feet — for daylight, energy and quantity planning.
A 36 × 60 inch window is about 15.0 square feet of glass (width × height ÷ 144, since 144 in² = 1 ft²). The daylight opening — the visible glass — is a little smaller than the frame outside dimension; use the frame size for rough sizing and the daylight opening only where a spec calls for it.
Calculator inputs
Window square footage is plane geometry: multiply width by height in inches, then divide by 144 (there are 144 square inches in a square foot). It is the number you need for a window-to-wall ratio, for a fenestration energy-savings estimate, and for tallying total glass across a whole house.
One distinction matters: the frame size (the outside of the unit) is a little larger than the daylight opening (the visible glass). Use the frame size for rough sizing and ordering; use the daylight opening only where a spec or an energy calc explicitly asks for visible glass area.
Formula
area_sqft = width_in × height_in ÷ 144
Because 12 in × 12 in = 144 in² = 1 ft², dividing the product of the two inch dimensions by 144 converts straight to square feet.
Worked example
For a 36 × 60 inch window:
area = 36 × 60 ÷ 144 = 2,160 ÷ 144 = 15.0 sq ft
Ten of those is 150 sq ft of glass — the figure you would drop into an energy-savings estimate or a window-to-wall ratio.
What to measure first & common mistakes
- Frame vs daylight opening. The visible glass is smaller than the frame — typically by a couple of inches each way. For area used in energy work, check whether the spec wants glass area or rough opening.
- Keep units consistent. Both dimensions must be in inches before dividing by 144. If you measured in feet, multiply width × height directly (no ÷ 144).
- Bay and bow windows. Add the individual glass panels; the projecting geometry means the wall opening and the glass area are not the same thing.
- Don’t confuse area with united inches. Area (a product ÷ 144) sizes glass and energy; united inches (a sum) sizes and prices the unit.
Reference table
Glass area of common nominal window sizes (labeled planning sizes — confirm the exact product).
| Nominal size | Glass area |
|---|---|
| 24 × 36 in | 6.0 sq ft |
| 24 × 48 in | 8.0 sq ft |
| 28 × 54 in | 10.5 sq ft |
| 30 × 36 in | 7.5 sq ft |
| 30 × 48 in | 10.0 sq ft |
| 30 × 60 in | 12.5 sq ft |
| 32 × 48 in | 10.7 sq ft |
| 32 × 54 in | 12.0 sq ft |
| 36 × 48 in | 12.0 sq ft |
| 36 × 54 in | 13.5 sq ft |
| 36 × 60 in | 15.0 sq ft |
| 36 × 72 in | 18.0 sq ft |
| 48 × 48 in | 16.0 sq ft |
| 48 × 60 in | 20.0 sq ft |
| 60 × 48 in | 20.0 sq ft |
| 72 × 60 in | 30.0 sq ft |