Plan skylight dimensions for safer daylight distribution and roof efficiency. Estimate suitable glazed area, unit count, and practical sizing for projects.
| Room | Floor Area (m²) | Orientation | VLT (%) | Units | Suggested Skylight Area (m²) |
|---|---|---|---|---|---|
| Living Room | 24.00 | North | 70 | 2 | 2.12 |
| Kitchen | 15.00 | East | 68 | 1 | 1.16 |
| Studio | 30.00 | West | 72 | 3 | 2.78 |
Floor Area = Room Length × Room Width
Planned Total Skylight Area = Planned Units × Unit Width × Unit Length
Recommended Skylight Area = Floor Area × Base Ratio × Orientation Factor × Room Use Factor × Glazing Factor × Margin Factor ÷ (Shaft Factor × Pitch Factor × VLT Factor × Reflectance Factor × Obstruction Factor)
The base ratio starts at 8% of floor area. Adjustment factors increase or reduce the final requirement. Deep shafts, low transmittance, low reflectance, and obstructions all require more glazed area.
Enter the room length, width, and ceiling height first. Add shaft depth and roof pitch next. Choose the skylight orientation, room use, and glazing type. Then enter light transmittance, reflectance, losses, safety margin, and planned unit sizes. Press the button to view the recommended skylight area above the form. Use the CSV and PDF buttons to save your result.
Skylight sizing affects comfort, brightness, and roof performance. A small unit may underdeliver daylight. An oversized unit may add glare, heat gain, and extra cost. Good sizing supports balanced natural light and practical construction detailing.
The first step is floor area. Larger rooms need more daylight area. Ceiling height also matters. Tall rooms can absorb more light before the space feels bright. A basic floor percentage helps create a reliable starting point for design work.
Not every skylight performs the same way. A deep shaft reduces useful daylight. Roof pitch changes light entry. Interior obstructions can block part of the incoming light. These losses should be included before selecting a final unit size.
Visible light transmittance is important. Higher values usually allow more daylight into the room. Glazing type also affects performance. Double and triple units may improve insulation, but they can slightly reduce visible light compared with simpler glass options.
Bright interior finishes can improve daylight distribution. Light walls and ceilings reflect more incoming light. Dark finishes absorb more light. That means rooms with lower reflectance may need slightly larger skylight openings for similar daylight results.
Room function changes daylight expectations. A studio or office often needs stronger daylight support. A bathroom or circulation space may need less. A calculator helps adjust the target without guessing. This improves consistency across multiple rooms.
After the calculation, compare the recommended total glazed area with your planned unit sizes. If the planned area is too low, increase unit count or dimensions. If it is too high, review glare, heat, waterproofing, and framing impacts.
This calculator supports early design and estimating. Final selection should also consider structure, flashing, roof layout, weather exposure, code requirements, and manufacturer data. Use the result to narrow options and improve project decisions with confidence.
A common starting point is about 5% to 10% of floor area. Final sizing changes with shaft depth, glazing, room use, and reflectance. This calculator adjusts those factors.
Deep shafts reduce daylight before it reaches the room. That means the skylight often needs more glazed area to deliver the same visible brightness.
Yes. Pitch affects how light enters the opening. It can also influence drainage, detailing, and product selection. Moderate changes can shift effective daylight delivery.
Visible light transmittance shows how much daylight passes through the glazing. Higher percentages usually mean better daylight entry, though other performance factors still matter.
No. Different room uses have different daylight needs. A studio or office often benefits from stronger daylight support than circulation or utility spaces.
Yes. Enter the planned number of units and each unit size. The calculator compares planned total area with the recommended total skylight area.
No. It is a planning tool. Final approval should also review structural framing, waterproofing, local code, product data, and installation requirements.
Add a safety margin when the room has daylight losses, uncertain finishes, or higher brightness expectations. It helps prevent undersizing during early planning.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.