Estimate roof surface area, roofing squares, shingle bundles and cost from the building size and pitch.
Roof area = footprint (with overhang) × pitch factor, where factor = √(1 + (pitch ÷ 12)²). A 40 × 30 ft building with 1 ft overhang and a 6:12 roof is about 1,503 sq ft — 15 squares, or 50 bundles with 10% waste.
The Roofing Calculator estimates how much roofing material you need. Enter the building's length and width, the eave overhang and the roof pitch (rise per 12 units of run). It returns the true sloping roof area, the number of roofing squares (100 sq ft each), the bundles of shingles with waste included, and an optional cost.
A sloped roof has more surface than the floor beneath it, so the footprint is multiplied by a pitch factor. This calculator assumes the same pitch on every slope (a simple gable or hip roof); add dormers, valleys and complex areas separately. Related: Square Footage Calculator and Tile Calculator.
Roof area follows from the footprint and the slope.
| Building and pitch | Roof area | Squares | Bundles |
|---|---|---|---|
| 40 × 30 ft, 1 ft overhang, 6:12 | 1,502.6 sq ft | 15.03 | 50 |
| same building at 4:12 | 1,416.7 sq ft | 14.17 | 47 |
| 12 × 9 m, 0.5 m overhang, 8:12 | 1,681.8 sq ft | 16.82 | 56 |
| 50 × 24 ft, 1 ft overhang, 9:12, 15% waste | 1,690 sq ft | 16.9 | 59 |
| Pitch (rise : 12) | Angle | Pitch factor |
|---|---|---|
| 2:12 | 9.5° | 1.0138 |
| 3:12 | 14.0° | 1.0308 |
| 4:12 | 18.4° | 1.0541 |
| 5:12 | 22.6° | 1.0833 |
| 6:12 | 26.6° | 1.1180 |
| 7:12 | 30.3° | 1.1577 |
| 8:12 | 33.7° | 1.2019 |
| 9:12 | 36.9° | 1.2500 |
| 10:12 | 39.8° | 1.3017 |
| 12:12 | 45.0° | 1.4142 |
Allow about 10% waste for a simple gable roof and 15–20% for hips, valleys and many cuts. Add the areas of dormers and extensions separately. Ridge caps, underlayment, drip edge and flashing are bought in addition to the main shingles.
Multiply the building's plan area (including overhang) by the pitch factor √(1 + (pitch/12)²). A 6:12 pitch has a factor of 1.118.
A roofing square is 100 square feet of roof (about 9.3 m²). Roofers quote material and labour per square.
Typically 3 bundles per square for standard 3-tab and architectural shingles; check the product label.
The rise in inches for every 12 inches of horizontal run. A 6:12 roof rises 6 inches per foot, an angle of 26.6°.
About 10% for simple roofs and 15–20% for complex ones with valleys, hips or dormers.
Yes. When every slope has the same pitch, a hip roof has the same surface area as a gable roof over the same footprint.
Yes — enter the eave overhang on each side so it is added to the footprint.
Yes — choose metres for the dimensions; area is shown in sq ft and m². Pitch is always rise per 12 units.
Underlayment, ridge caps, starter strips, drip edge, flashing and nails, in addition to shingles.
No. Everything runs in your browser.
