Skip to main content
Calcimator

Skylight Sizing Calculator

Calculate optimal skylight area, roof percentage, daylight factor, and heat gain impact for natural daylighting design.

Inputs

sq ft
ft
%
°
°

Results

Skylight Area Needed

23.67 sq ft

≈ 35 sheets of paper

Achieved Daylight Factor

5%

Skylights Needed (2×4)

3

Roof Opening Percentage5.92%
Peak Heat Gain7,101 BTU/hr
How to Use This Calculator
  1. Enter the Room Floor Area in sq ft and the Ceiling Height in feet.
  2. Enter the Target Daylight Factor percentage (2% = dim, 5% = well-lit, 10% = very bright).
  3. Enter the Roof Slope in degrees and your Latitude.
  4. Review Skylight Area Needed in sq ft and Recommended Count based on standard 2×4 ft units.
  5. Check Achieved Daylight Factor and Peak Heat Gain in BTU/hr for energy impact assessment.

How the result changes with Room Floor Area

Room Floor AreaSkylight Area NeededAchieved Daylight FactorSkylights Needed (2×4)
1,00059.18 sq ft5%8
3,500207.12 sq ft5%26
6,500384.66 sq ft5%49
9,000532.61 sq ft5%67

What each input means

Room Floor Area
Floor area of the room to be daylit.
Ceiling Height
Floor-to-ceiling height (taller rooms need more skylight area).
Target Daylight Factor
Desired daylight factor percentage (2% = dim, 5% = well-lit, 10% = very bright).
Roof Slope
Roof pitch in degrees (0 = flat, 30 = moderate pitch).
Latitude
Location latitude (higher latitudes get less direct sun).

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Room Floor Area = 400, Ceiling Height = 8, Target Daylight Factor = 5, Roof Slope = 30 = 5 input(s) provided
  2. Calculate Skylight Area Needed
    Skylight Area Needed
    23.67 = 23.67
  3. Calculate Achieved Daylight Factor
    Achieved Daylight Factor
    5 = 5
  4. Calculate Skylights Needed
    Skylights Needed
    3 = 3
  5. Calculate Roof Opening Percentage
    Roof Opening Percentage
    5.92 = 5.92
  6. Calculate Peak Heat Gain
    Peak Heat Gain
    7101 = 7101

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Glazing & Windows

Window U-Factor Calculator

Calculate overall window U-factor from frame and glass components, with R-value, annual heat loss, and energy cost impact.

Glazing & Windows

Solar Heat Gain Calculator

Calculate solar heat gain through windows based on SHGC, orientation, latitude, and shading to estimate cooling load impact.

Green Building

Daylighting Factor Calculator

Calculate the Average Daylight Factor for a room based on window area, glass transmittance, room geometry, and surface reflectance.

Glazing & Windows

Glass Thickness Calculator

Determine minimum glass thickness based on wind load, panel dimensions, glass type, and elevation with safety factor analysis.

More in Construction & Building Trades.