Estimate sloping roof area and bundle equivalents from the coverage stated for your chosen shingles. For an initial material estimate on a simple roof with one pitch. With a symmetrical gable roof, use the full horizontal width to represent both slopes together.
- Plan length and full width
- Horizontal dimensions of the area covered, not dimensions measured along the slope.
- Pitch and allowance
- Slope angle in degrees and a separately chosen material allowance.
- Coverage per bundle
- Installed coverage in m² per bundle, or ft² in imperial mode, from the product packaging.
Enter one rectangle and one pitch. Split a roof with several pitches or non-rectangular regions into suitable separate area estimates.
- Sloping area, material equivalents before allowance and equivalents after allowance.
A simple roof with a chosen 15% allowance. In this example, each material unit covers 3 m².
| Quantity | Value |
|---|---|
| Plan length × full width; pitch | 10 × 8 m; 30° |
| Coverage per unit; allowance | 3 m²; 15 % |
| Sloping area | 92.376 m² |
| Base equivalents | 30.79 |
| Bundle equivalents, with allowance | 35.41 |
Area = length × width / cos(angle). Divide by 3 m², then multiply by 1.15. Figures are shown to two decimals for the material count. The unrounded result is about 35.411; rounding that quantity up gives 36 whole units before any layout-specific additions.
If a drawing gives slope as rise over horizontal run, convert that ratio before entering the roof angle. A 6:12 slope means 6 units of vertical rise per 12 of horizontal run, measured in the same units. It is 50%, not 6° or 12°.
Angle = atan(rise ÷ horizontal run), expressed in degrees. For 6:12, atan(6 ÷ 12) ≈ 26.565°. Enter that angle in this Pro² roof tool. You can also open Tools → Slope finder with the actual rise and horizontal run, then carry its angle into the roof calculation.
Use the horizontal run of one slope for the ratio. On a symmetrical gable roof, it is half the total span, not the sloping rafter length. The roof-area width field still follows the full-plan-width convention described above. This conversion does not choose a suitable slope or approve a roofing product.
Metric and imperial dimensions are supported. Pitch is an angle in degrees, not rise-per-12 or a percentage. The area method assumes one pitch over the plan rectangle.
The chosen allowance is not a guaranteed waste rate. Hips, valleys, openings, starter pieces, ridge pieces, flashings and fasteners need a separate takeoff.
Coverage varies by product. The app displays a fractional bundle estimate; purchasing whole bundles requires rounding up after applying the chosen allowance. Separate starter and ridge products are not included.
This tool estimates covering material. It does not size rafters, check roof loads or design the roof structure.
Does every bundle cover the same area?
No. Use the installed coverage printed for the particular shingles, not a generic bundle size.
Do I halve the width of a gable roof?
Not when estimating both equal slopes together. The full plan width already covers both halves; calculate only one half if you intend to estimate one slope.
- Does every bundle cover the same area?
- No. Use the installed coverage printed for the particular shingles, not a generic bundle size.
- Do I halve the width of a gable roof?
- Not when estimating both equal slopes together. The full plan width already covers both halves; calculate only one half if you intend to estimate one slope.
Measurements, units and material terms
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