Window-to-Floor Ratio

Calculate window-to-floor ratio and estimated daylight factor for any room. Check against building regulation minimums.

Room Dimensions

Length

Width

Ceiling height

Windows

Total glazed area 0.00 m²

Glazing Properties

Glazing type

Room use

Results

Enter dimensions

Floor area

—

m²

Glazed area

—

m²

WFR

—

Est. Daylight Factor

—

Daylight Quality

Poor (<1%)Adequate (2%)Good (>5%)

WFR Targets

Habitable room (UK)

WFR ≥ 20% DF ≥ 2%

Office (CIBSE)

WFR ≥ 20% DF ≥ 2%

Classroom

WFR ≥ 20% DF ≥ 3%

Hospital ward

WFR ≥ 25% DF ≥ 2%

Industrial (min)

WFR ≥ 10% DF ≥ 1%

Daylight Factor Formula

Simplified BRE formula:


DF ≈ (Aw × τ × θ) / (A × (1 − R²))

Where Aw = glazed area, τ = transmittance, θ = sky angle (assumed 40°), A = total room surface area, R = average reflectance (assumed 0.5).

Room Depth Rule

For adequate side lighting, room depth should not exceed 2.5× the window head height from the window wall. Deeper rooms need rooflights or supplementary artificial lighting.