Formula Used
This calculator supports two common definitions, using an optional frame factor.
- Effective Window Area = Entered Window Area × Frame Factor
- Gross WWR (%) = (Σ Effective Window Area ÷ Σ Gross Wall Area) × 100
- Net Wall Area = Gross Wall Area − Door Area − Other Openings Area
- Net WWR (%) = (Σ Effective Window Area ÷ Σ Net Wall Area) × 100
Practical note: Some standards use gross wall area, others use net. Select the method that matches your project reporting rules.
How to Use This Calculator
- Choose Gross or Net calculation method.
- Set a frame factor if window area includes frames.
- Enter each façade’s gross wall area and window area.
- If using net method, also enter door and other openings.
- Click Calculate WWR to view results above.
- Use the download buttons to export CSV or PDF.
Example Data Table
| Facade | Orientation | Gross wall (m²) | Door (m²) | Other (m²) | Window (m²) |
|---|---|---|---|---|---|
| 1 | North | 120 | 6 | 0 | 36 |
| 2 | East | 110 | 3 | 0 | 28 |
| 3 | South | 130 | 4 | 0 | 52 |
These sample values are prefilled in the form so you can test quickly.
Window-to-Wall Ratio: Practical Guidance for Building Envelopes
1) Why Window-to-Wall Ratio Matters
Window-to-wall ratio (WWR) expresses glazing area as a share of exterior wall area. It strongly influences heating and cooling loads, peak demand, daylight availability, and glare risk. A higher WWR often increases solar gains and conductive losses unless high-performance glazing is used.
2) Data Inputs That Drive Accuracy
Reliable WWR begins with consistent area takeoffs. Use gross wall area from elevations, then confirm window openings from schedules. If doors and other penetrations are significant, net wall reporting can better match façade performance studies. Keep all inputs in one unit system to avoid scaling errors.
3) Interpreting Gross vs Net WWR
Gross WWR compares effective window area to gross wall area and is common for high-level envelope reporting. Net WWR removes doors and other openings from the denominator, producing a slightly higher percentage for the same glazing. This is useful when comparing only opaque wall versus glazing on an elevation.
4) Design Benchmarks and Climate Considerations
Many teams set a target range (for example, 30–45%) early in design. In hot climates, lower WWR on east and west façades can reduce morning and afternoon heat gains. In colder climates, balanced WWR with optimized U-values and solar heat gain coefficients can improve comfort without excessive energy penalties.
5) Reporting and Coordination Tips
Track WWR by orientation to support shading studies and façade optimization. Apply a frame factor if your window areas include frames, spandrels, or mullions, so the “effective” glazed area aligns with your performance modeling convention. Exporting CSV and PDF summaries helps coordinate architects, MEP engineers, and energy analysts using the same snapshot of data.
FAQs
1) What is the window-to-wall ratio?
WWR is the percentage of window area compared with exterior wall area. It is calculated as window area divided by wall area, multiplied by 100.
2) Should I use gross or net WWR?
Use gross WWR for standard reporting against elevation wall area. Use net WWR when you want the denominator to exclude doors or other openings and focus on opaque wall versus glazing.
3) What is the frame factor used for?
Frame factor adjusts window area to an effective glazing area. If your takeoff includes frames or mullions, a factor below 1.00 can better reflect the glass portion used for performance comparisons.
4) Can I mix units like m² and ft²?
No. Keep all areas in the same unit system. The ratio is unitless, but mixing units will distort the denominator and produce incorrect percentages.
5) Why track WWR by orientation?
Orientation affects solar exposure and glare. Separating north, east, south, and west façades helps identify where glazing should be reduced, shaded, or upgraded to meet energy and comfort goals.
6) What does “Above target” mean?
It indicates a façade WWR higher than your selected maximum target. It is a quick flag for review, not a pass/fail code check.
7) How should I use the exported files?
Use the CSV for quick sharing, filtering, and QA checks. Use the PDF summary for submittals, design reviews, and meeting notes where a compact, readable snapshot is preferred.