Window-to-Wall Ratio Calculator
List the walls and the windows on each, and the window to wall ratio calculator shows the glazed share of every wall and the ratio for all of them together. Add the floor size to get the window-to-floor ratio as well, and enter your own target if your rules or brief give one.
Window-to-wall ratio calculator
Planning aid, not an energy or daylight compliance check. Methods (frame or glass, gross or net wall) differ; use the one your rules specify.
A label for your result; enter the sizes your method asks for
Leave blank (or 0) to skip the window-to-floor ratio
Leave blank (or 0) to skip the window-to-floor ratio
Assumptions
Change any value to match your product or local rules.
Leave blank (or 0) for none, e.g. a figure from your energy rules
Basis: No default figure: limits and targets differ by jurisdiction, building type and method; enter yours if you have one.
- Window-to-wall ratio
- 22.2%
- Window area
- 3.60 m²
- 38.8 sq ft
- Gross wall area
- 16.20 m²
- 174.4 sq ft
- Window-to-floor ratio
- 23.8%
- Against your target
- No target entered
Windows (frame sizes) cover 3.60 m² (38.8 sq ft) of 16.20 m² (174.4 sq ft) of wall: 22.2%.
Each wall
- Wall 1 (6.00 m × 2.70 m): 22.2%
How this was calculated
- Window-to-wall ratio = Σ window area ÷ Σ gross wall area × 100 % (per wall: that wall’s windows ÷ that wall)
- Window-to-floor ratio = Σ window area ÷ floor area × 100 %
- Wall 1 = (1.50 m × 1.20 m × 2) ÷ (6.00 m × 2.70 m) = 3.60 m² ÷ 16.20 m² = 22.2%
- Window-to-wall ratio = 3.60 m² ÷ 16.20 m² × 100 % = 22.2%
- Floor area = 4.20 m × 3.60 m = 15.12 m²
- Window-to-floor ratio = 3.60 m² ÷ 15.12 m² × 100 % = 23.8%
How the ratio is worked out
Wall area
Each wall is its length times its height, measured gross: windows are not taken out.
Window area
Each window is its width times its height times how many, counted on the wall you put it on.
Per wall
A wall’s ratio is its windows’ area divided by its own area, as a percentage.
Overall and per floor
The overall ratio divides all the window area by all the wall area. The window-to-floor ratio divides the same window area by the floor area.
Worked example in meters and in feet
A facade 6.0 m long and 2.7 m high has 16.2 m² of wall. Two windows of 1.5 × 1.2 m add up to 3.6 m², so the window-to-wall ratio is 3.6 ÷ 16.2 = 22.2 %. If the room behind it is 4.2 × 3.6 m (15.12 m²), the window-to-floor ratio is 3.6 ÷ 15.12 = 23.8 %.
In feet, a wall 20 ft long and 9 ft high is 180 sq ft. Two 5 × 4 ft windows are 40 sq ft: 40 ÷ 180 = 22.2 %. Over a 14 × 12 ft floor (168 sq ft), that is 23.8 % window-to-floor.
What window-to-wall ratio measures
The ratio says how much of a wall is glass (or window) rather than solid wall. Designers use it to talk about how open a facade is, and energy and daylight methods use it because windows usually let more heat through than solid wall and let light in.
The figure on its own is neither good nor bad. More glass brings more daylight and view; it can also mean more heat lost in winter and gained in summer, depending on the glazing, shading and orientation.
Window-to-wall or window-to-floor?
They answer different questions and are easy to mix up. Window-to-wall compares glazing with the wall it sits in, so it describes a facade. Window-to-floor compares glazing with the floor of the room behind it, so it is closer to how much daylight and ventilation the room might get. A tall wall with the same windows has a lower window-to-wall ratio but the same window-to-floor ratio.
Gross wall area and what counts as window
Methods differ on two points: whether the window is measured at the frame (the rough opening) or as visible glass only, and whether the wall is taken floor to floor or floor to ceiling. The calculator works with whatever you enter, and the “measured as” choice labels the result so you remember which you used.
Glazed doors, rooflights and curtain walling may or may not count depending on the method. If your method counts a glazed door, enter it as a window on its wall.
One wall, a room or a whole building
For one facade, enter a single wall. For a room, enter its walls and put each window on the wall it is in; walls with no windows still count in the overall ratio. For a whole building, list each elevation as one wall with its full length and height. The per-wall figures show where the glazing is concentrated, which an overall figure hides.
Frequently asked questions
How do you calculate window-to-wall ratio?
Add up the area of the windows and divide by the gross area of the walls they sit in (length × height, with no openings taken out). Multiply by 100 for a percentage. Two 1.5 × 1.2 m windows in a 6 × 2.7 m wall give 3.6 ÷ 16.2 = 22.2 %.
What is the difference between window-to-wall and window-to-floor ratio?
Window-to-wall divides window area by the wall area it sits in. Window-to-floor divides the same window area by the floor area of the room. The calculator shows both from one set of windows.
Do I measure the frame or the glass?
Whichever your method asks for. Methods differ: some use the frame or rough opening, others glass only. Use the one your rules specify, measure the same way throughout and pick the matching “measured as” option so the result is labelled.
Do doors with glass count?
It depends on the method you are following. If it counts glazed doors as windows, enter them as windows on their wall; if not, leave them out.
Is a higher window-to-wall ratio better?
Not in itself. More glazing can bring more daylight and view but also more heat loss and gain. The right balance depends on the glazing, shading, orientation and the rules or brief you are working to.
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