Skylight Area – Size, Shaft & Light Gain

A reliable skylights takeoff follows one rule: measure twice, order once. The calculator converts your floor area below and roof pitch into dependable quantities using Skylight Area = Floor × 7%; Light Gain ≈ 3× same-area window, then adds the waste margin that experienced builders apply by default. Example: A 20 m² bathroom: 1.4 m² skylight - one 0.78 × 1.16 m unit at 0.65 m² net leaves room for two. Field tip: North-light skylights give even daylight; south-facing ones double as solar heaters. The result is broken down into purchasable units - bags, sheets, rolls or truck loads - so you can order the nearest whole unit without overbuying, and every figure traces back to the formula shown above.

1. 1

   Measure the space

   Record the floor area below and roof pitch at the widest and longest points.

2. 2

   Enter the values

   Type the measurements into the calculator and select your units.

3. 3

   Apply the formula

   The tool computes Skylight Area = Floor × 7%; Light Gain ≈ 3× same-area window for your inputs instantly.

4. 4

   Add waste and order

   Review the total with a 5-10% margin and round up to whole units.

• Ordering exact sheet count

• Compressing insulation

• Vapor barrier on the wrong side