Roof Shingle & Area Calculator
Enter the building footprint, the pitch, the shingle type and the waste allowance. The page returns the sloped roof area, roofing squares, bundles of shingles, underlayment rolls and nails.
Roof area is never the footprint. Measure the building, pick the pitch, and the page returns the sloped surface, the roofing squares, the bundles, the underlayment rolls and the nails — before you order.
The building
Measure wall to wall in metres and include the eaves overhang. Pitch is expressed as rise over 12 of run.
Roof area
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Roofing squares
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Bundles of shingles
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Underlayment rolls
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Roofing nails
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Pitch factor
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How this was worked out
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Pitch reference
| Pitch | Angle | Factor | Notes |
|---|---|---|---|
| 4/12 | 18.4° | 1.054 | Minimum pitch for standard three-tab. Full underlayment is required. |
| 6/12 | 26.6° | 1.118 | The most common pitch. Standard practice for most homes. |
| 8/12 | 33.7° | 1.202 | Better drainage. Steeper roofs shed water and debris faster. |
| 10/12 | 39.8° | 1.302 | Steep. Use roof jacks and a harness; bundles slide. |
| 12/12 | 45° | 1.414 | 45°. Very steep; allow extra labour and full underlayment. |
100 m² of footprint at each pitch
| Pitch | Roof area | Three-tab bundles |
|---|---|---|
| 4/12 | 105.4 m² | 38 |
| 6/12 | 111.8 m² | 40 |
| 8/12 | 120.2 m² | 43 |
| 10/12 | 130.2 m² | 47 |
| 12/12 | 141.4 m² | 51 |
Five rules for the order
- Pitch sets the area, not the footprint. A 6/12 roof has 1.118 times the footprint; a 12/12 roof has 1.414 times.
- One roofing square is 100 square feet, or 9.29 m². Suppliers price in squares, so convert before you call.
- Three-tab shingles need 3 bundles per square; architectural shingles need 4. Read the wrapper, not the shelf talker.
- Start at 10% waste for a simple gable. Use 15% for hips, valleys and dormers, and keep one bundle spare.
- Underlayment and nails scale with squares: one roll per 2 squares, about 320 nails per square.
Practical notes
- Measure the overhang. Most roofs extend 30–60 cm past the wall, and that strip adds area on all four sides.
- Measure the flat footprint, then apply the pitch factor once. Measuring along the rake and multiplying again doubles the slope.
- Order underlayment by the roll and check coverage: a 1 × 33 m roll covers about 2 squares once the laps are counted.
- Nails run about 320 per square for field shingles. Add more for hips, ridges and starter strips.
Four common mistakes
- Using the floor area as the roof area. A 12 × 8 m footprint is 96 m², but a 6/12 roof is 107 m² before waste.
- Forgetting waste on hips and valleys. Every valley doubles the cutting and the offcuts.
- Mixing bundle counts between shingle types. Four bundles of three-tab is 1.33 squares, not 1.
- Ordering nails by the box without counting squares. Two boxes may be enough, or three short.
Figures are ordering estimates. Confirm load capacity and installation with local building codes and the product data sheet, and take care with ladders and work at height.