Window-to-Wall Ratio Calculator
Enter the external wall area and total window area to calculate the window-to-wall ratio (%), and check it against an optional maximum allowed ratio. A Hong Kong building energy-efficiency and daylight indicator.
Input Data
Results
At a glance:Window-to-Wall Ratio (WWR) = total window area ÷ total external wall area × 100%, reflecting how transparent the façade is. A high ratio gives good daylight and views but increases heat gain, cooling load and glare, so energy-conscious design often sets an upper limit. Hong Kong's BEAM Plus and building energy-efficiency frameworks watch envelope performance, of which WWR is one indicator; the actual limit depends on the project standard and regulations, not a single statutory number.
Formula
WWR = window area / external wall area × 100%
Compliant if WWR ≤ limit
$$WWR = \frac{A_w}{A_s}\times 100\%$$$$WWR \le WWR_{\max}$$How to Use
- Enter the external wall area (m²).
- Enter the total window area (m²).
- Optionally enter the allowed maximum (%).
- The tool outputs the WWR and check.
Case Studies
Residential façade
Wall 20 m², windows 6 m².
WWR 30%; compliant at a 40% limit.
Shopping-mall curtain wall
Wall 100 m², windows 80 m².
WWR 80%; exceeds a 60% limit, needs adjustment.
FAQ
What does a high WWR do?
Good daylight and views, but more heat transfer and cooling load and more glare; energy design must balance them.
Who sets the limit?
It follows the green-building standard adopted (e.g. BEAM Plus) or relevant energy-efficiency requirements; there is no single statutory value.
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References
Content review: Calculatorism Construction Team. Results are for reference only; please refer to the relevant authorities for the official figures.