Daylight Ratio Calculator
Window-to-floor ratios for natural light
Daylight meter
Habitable-room glazing minimums vary by code and climate — always check your local building regulations.
About Daylight Ratio Calculator
The daylight ratio calculator checks whether a room gets enough natural light by comparing its glazing area to its floor area. Enter the room’s floor area, then add each window with its width and height — the tool totals the glass, divides by the floor area, and gives a window-to-floor ratio with a verdict.
The window-to-floor ratio is the classic quick test used in housing codes and early design: many jurisdictions require somewhere around 10% glazing-to-floor for habitable rooms as a bare minimum, while well-daylit rooms commonly reach 15–20%. The verdict scale runs from insufficient through bare minimum and good to excellent, with a daylight meter that fills as you add glass.
Use it when sketching a floor plan, sizing windows for an extension, or checking a bedroom conversion. You can add and remove any number of windows and see the ratio update live, free in your browser. Habitable-room glazing minimums vary by code and climate, so always check your local building regulations.
How to use Daylight Ratio Calculator
- Enter the room’s floor area.
- Add each window and fill in its width and height; use “Add window” for more openings.
- Read the total glazing area and the window-to-floor ratio.
- Check the daylight meter and verdict, and resize windows until the rating satisfies you.