Roofing & Solar
The top of your house does two jobs: it keeps the weather out, and it can quietly power the home under it. Start with how much usable roof you have.
Calculators for This Category
- Roofing Materials Roofing & Solar Footprint and pitch to a full shingle order — squares, bundles, underlayment, ridge caps, drip edge and nails, waste included.
- Solar Panel System Sizing Roofing & Solar Panel count from roof area, system size in kW, and annual kWh production — with sun-hours and efficiency loss built in.
- Gutter & Downpipe Roofing & Solar Eave run and roof width in — gutter length, catchment area, downpipe count and brackets out.
- Solar Battery Sizing Roofing & Solar Daily usage and backup days in — bank capacity in kWh and Ah at 12, 24 or 48 V out.
Practical Guides
- Roof Area: How Roofers Measure a Roof Roofing Footprint, pitch multipliers, waste factors and squares — measured from the ground, ordered with confidence.
- How Many Solar Panels Fit on Your Roof? Solar Usable area, setbacks, and the arithmetic from square feet to kW — sized to the bill, not just the roof.
- Attic Ventilation: How Much You Need Roofing The IRC ratios, net free area, and the soffit-to-ridge balance that keeps an attic healthy.
- Gutters and Downpipes: Sizing and Layout Catchment area with the pitch multiplier, outlet placement, falls and bracket spacing.
Solar planning and roofing are the same measurement problem: how much usable, structurally sound roof area do you have? Panels live on the roof, so start with the roof. The roofing materials calculator turns footprint and pitch into a shingle order, and the solar sizing calculator handles tilt, shading and efficiency losses once you know your area.
Roof Pitch Multiplication Factors
Roof area is bigger than its footprint. Measure the building footprint (length × width), then multiply by the factor for your pitch. These multipliers are the standard published values used across the roofing industry.
| Roof pitch | Angle | Multiplier |
|---|---|---|
| 4 / 12 | 18.4° | 1.054 |
| 6 / 12 | 26.6° | 1.118 |
| 8 / 12 | 33.7° | 1.202 |
| 10 / 12 | 39.8° | 1.302 |
| 12 / 12 | 45.0° | 1.414 |
Typical residential guidance only — a roof replacement, structural load check or grid connection should always be confirmed with a qualified roofer or engineer.