Estimate sloping area and the equivalent number of sheets by area. Confirm whole sheets, laps and layout with the supplier. 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.
- Sheet width and length
- The two dimensions are multiplied directly. The app does not deduct side or end laps automatically.
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° |
| Sheet width × length | 1 × 3 m |
| Coverage per unit; allowance | 3 m²; 15 % |
| Sloping area | 92.376 m² |
| Base equivalents | 30.79 |
| Sheet 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.
This is an area estimate, not a row-by-row sheet layout. If you use nominal full sheet dimensions, overlap is not deducted. A useful-coverage estimate needs effective dimensions justified by the product and laying direction.
This tool estimates covering material. It does not size rafters, check roof loads or design the roof structure.
Can I order the displayed number of sheets?
Use it as an area equivalent. Confirm whole sheets, lengths, laps and the actual arrangement with the supplier; rounding the area ratio alone cannot prove the layout fits.
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.
- Can I order the displayed number of sheets?
- Use it as an area equivalent. Confirm whole sheets, lengths, laps and the actual arrangement with the supplier; rounding the area ratio alone cannot prove the layout fits.
- 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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