Window-to-wall ratio (WWR) calculator

Divide total glass area by gross wall area to get the window-to-wall ratio — a daylight and energy planning number.

Measure each opening and confirm sizes and clearances against the exact product you buy. Take three width and three height measurements and use the smallest of each; allow extra for custom sizes and waste. Sizes, clearances and rough-opening allowances vary by product and brand — read the spec sheet and the manufacturer’s data.
Your result
Window-to-wall ratio9.5 %
Total window area120 sq ft
Gross wall area1,260 sq ft (140 ft × 9 ft)

120 sq ft of glass against 1,260 sq ft of gross wall is a window-to-wall ratio of about 9.5% (typical US homes run ~10–20%). WWR is a daylight/energy planning number — it is not a code compliance calc; energy code sets fenestration U-factor and area limits, so confirm locally.

Calculator inputs

sq ft
ft
ft

Window-to-wall ratio (WWR) is the share of a building’s exterior wall taken up by glass. It is a daylight and energy planning number: more glass means more daylight and solar gain but more heat loss, so architects and energy programs watch it. Most US houses land somewhere around 10–20%.

To use it, add up your total window glass area, then estimate the gross wall area as the exterior wall perimeter times the wall height. The ratio of the two is your WWR.

Formula

gross_wall_area = wall_perimeter_ft × wall_height_ft
WWR = total_window_area ÷ gross_wall_area

The result is a fraction; multiply by 100 for a percentage.

Worked example

Eight windows at 15 sq ft each is 120 sq ft of glass. A 140 ft perimeter with 9 ft walls is 1,260 sq ft of gross wall:

WWR = 120 ÷ (140 × 9) = 120 ÷ 1,260 = 0.095 → 9.5%

That is a modest, energy-friendly ratio — typical for a conventional home.

What to measure first & how to read WWR

  • Gross wall means the whole wall. Use the full exterior wall area (perimeter × height), including the parts behind windows and doors — that is the convention WWR uses.
  • One story or whole house. Be consistent: if you use whole-house glass area, use whole-house wall area (add each story’s perimeter × height).
  • WWR is planning, not code. Energy codes limit fenestration by U-factor and by area in their own way; a WWR number here does not certify code compliance — confirm locally.
  • High WWR needs better glass. If your ratio is on the high side, low-U, climate-appropriate SHGC glazing matters more — see the ENERGY STAR climate-zone checker.

Reference table

Typical window-to-wall ratios (labeled planning ranges — not a code limit).

Design intentWWR
Conservative / energy-focused~10% or less
Typical US home~10–20%
Daylight-optimized / modern~20–30%
Glass-forward (curtain-wall look)30%+

Frequently asked questions

What is a good window-to-wall ratio?
Most US homes run about 10–20%. Lower ratios favor energy efficiency; higher ratios favor daylight and views but need better-performing glass to control heat loss and gain.
How do I calculate window-to-wall ratio?
Divide the total window glass area by the gross wall area (exterior wall perimeter × wall height). 120 sq ft of glass on 1,260 sq ft of wall is a 9.5% WWR.
Does gross wall area include the windows?
Yes. Gross wall area is the entire exterior wall, including the area occupied by windows and doors. That is the standard basis for WWR.
Is window-to-wall ratio a code requirement?
Not directly. Energy codes regulate fenestration through U-factor and area limits in their own terms. WWR is a planning metric — confirm any code limits with your local building department.

Related calculators

Window area (square footage)Convert window width and height (inches) to glass area in square feet: width × height ÷ 144. Worked example, a size chart and the frame-vs-daylight difference.Window energy-savings estimatorEstimate annual heating-season savings from lower-U-factor windows: area × ΔU × heating-degree-days × 24 ÷ 1000 ÷ efficiency × your energy price.ENERGY STAR climate-zone checkerCheck a window U-factor and SHGC against ENERGY STAR 7.0 and IECC 2021 requirements by climate zone, with a Meets / Does not meet verdict for each snapshot.Window count calculatorCount the windows in a house room by room to get the total openings to order and budget. Worked example, a windows-by-home-size chart and how to count bays.