Skylight Calculator
Estimate skylight area and recommended size
Floor area of the room to be daylit
Ceiling height of the room
Recommended Size
—
ft
Skylight Area
—
sq ft
Ceiling Height
—
ft
Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor, engineer, or architect. Verify all calculations before making purchasing or construction decisions.
How to Use This Calculator
Adding a skylight brings in natural daylight and cuts lighting costs. Our calculator sizes the glazing area to about 10% of the room floor, then matches it to the nearest standard skylight.
- Measure the floor area of the room
- Enter the ceiling height
- Run the calculator
- Choose a venting or fixed skylight based on the recommended size
Expert Insights
Smart analysis for your Skylight project
Daylighting Ratio Guidance
A 10% glazing-to-floor ratio balances daylight and heat gain. South-facing skylights may need less area; north-facing may need more.
Shaft & Ceiling Height
Taller ceilings create longer light shafts that spread daylight wider. AI accounts for ceiling height when sizing the opening.
Energy & Glazing Selection
Low-E double-pane skylights cut heat loss by 30-50%. AI recommends ENERGY STAR glazing for your climate zone to prevent overheating.
Calculation Formula
Skylight area = Room area x 0.10
Recommended size = nearest standard skylight:
<= 4 sq ft: 2x2 ft
<= 8 sq ft: 2x4 ft
<= 12 sq ft: 3x4 ft
<= 16 sq ft: 4x4 ft
<= 24 sq ft: 4x6 ft
> 24 sq ft: multiple skylights recommended
Skylight Type Comparison
| Skylight Type | Ventilates | Cost Range | Glazing | Best For |
|---|---|---|---|---|
| Fixed | No | $150-$500 | Single/Double | Daylight only |
| Manual Venting | Yes (hand crank) | $250-$700 | Double | Kitchens, baths |
| Electric Venting | Yes (motorized) | $400-$1,200 | Double/Low-E | Hard-to-reach |
| Tubular (Sun Tunnel) | No | $200-$600 | Acrylic dome | Small spaces, hallways |
Authority References
Our calculations are based on guidelines and standards from these authoritative sources:
- National Fenestration Rating Council (NFRC) — Skylight Energy Performance Ratings. Learn more
- ENERGY STAR — Skylight Product Specifications. Learn more
- International Residential Code (IRC) — Section R308 — Glazing & Skylight Installation. Learn more
Frequently Asked Questions
How big should a skylight be for a room?
A common rule is skylight area equal to 5-15% of the room's floor area. For general daylighting, use 10% as a starting point, then match to the nearest standard skylight size.
What are standard skylight sizes?
Common skylight sizes include 14x14, 16x16, 2x2, 2x3, 2x4, 3x4, 4x4, and 4x6 feet. Larger daylighting needs often use multiple units rather than one oversized skylight.
Do skylights add value to a home?
Yes. ENERGY STAR skylights can improve daylighting and ventilation, potentially raising home value by 3-5% while cutting lighting costs. Quality installation is key to avoiding leaks.