Roofing Calculator
Free roofing calculator. Estimate roof surface area from footprint and pitch, get shingle bundles, roof sheets, underlayment rolls, roofing squares, and cost.
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What is Roofing Calculator?
The Roofing Calculator is a free, browser-based tool that estimates the surface area of a gable or hip roof and converts it into the materials you need to buy. Enter the building footprint length and width plus the roof pitch — rise per 12 in imperial units, or the slope angle in degrees in metric — and the calculator applies the correct pitch multiplier, adds your waste allowance, and returns shingle bundles (or roof sheets), underlayment rolls, roofing squares, and an optional cost estimate. All math runs 100% client-side — no sign-up, no data uploads.
Key Benefits
- Accurate roof area from just two footprint measurements and the pitch — no climbing required
- Pitch multiplier handles any slope, from flat roofs to steep 12/12 and beyond
- Switch between shingle bundles and roof sheets to match how your supplier sells material
- Underlayment rolls, roofing squares, and both ft² and m² together for easy quoting
- Waste factor and per-unit costs built in, so your material list is ready to order
- 100% client-side and offline-capable — your project data stays private
Common Use Cases
- •Estimating shingle bundles for a re-roof quote before calling suppliers
- •Ordering metal or polycarbonate roof sheets with the right sheet length
- •Sizing underlayment and felt rolls for a new build or extension
- •Checking a contractor's material list against your own numbers
- •Converting between roofing squares, ft², and m² for international suppliers
How to Use the Roofing Calculator
- Measure the footprint: Measure the length and width of the building footprint (not the roof itself) at ground or eave level. Choose Imperial (feet) or Metric (meters) to match your tape measure.
- Enter the roof pitch: Enter the pitch: rise per 12 units of run in imperial mode (e.g. 6 for a 6/12 roof), or the slope angle in degrees in metric mode. The pitch multiplier is applied automatically.
- Pick shape and material: Choose Gable or Hip for the roof shape, then Shingles or Sheets for the covering. Set bundles per square (imperial) or bundle coverage in m² (metric), or the effective sheet width for sheet materials.
- Read and copy the estimate: See roof area, roofing squares, bundles or sheets to buy, and underlayment rolls. Optionally enter unit costs for a total material cost, then copy the full breakdown.
Key Features
- Gable and hip roof shapes with automatic ridge-length adjustment
- Pitch entry as rise per 12 (imperial) or slope degrees (metric)
- Shingle bundles per square or metric bundle coverage, fully adjustable
- Sheet mode: sheet length (eave to ridge) and sheet count from effective width
- Underlayment rolls, roofing squares, and both ft² and m² shown together
- Optional per-bundle / per-sheet and per-roll costs give a total project estimate
Frequently Asked Questions
How is roof area calculated from the footprint?
The calculator multiplies the building footprint (length × width) by the pitch multiplier, which is √(12² + rise²) / 12 for an imperial rise-per-12 pitch, or 1 / cos(angle) for a slope in degrees. A 40×20 ft footprint at 6/12 gives 800 × 1.118 ≈ 894 ft².
What is a roofing square?
One roofing square is 100 ft² of roof area — the unit suppliers quote shingles in. Most architectural shingles need about 3 bundles per square, so an 8.94-square roof needs roughly 27 bundles before waste.
How do I convert pitch rise-per-12 to degrees?
degrees = atan(rise / 12) × 180 / π. For example, 6/12 is atan(0.5) ≈ 26.57°, and 12/12 is 45°. The metric mode of this calculator accepts the angle directly.
Why is the hip roof ridge shorter than the building length?
A hip roof slopes on all four sides, so the horizontal ridge shrinks to length − width (and can be zero on a square hip roof). The surface area formula footprint × pitch multiplier still holds for a regular hip with equal pitch on all sides.
How much waste should I add?
10% covers cuts and starter courses on simple gable roofs; use 15% for hip roofs (more diagonal cuts at hips and valleys) and up to 20% for complex roofs with dormers, valleys, or chimneys.