From roof faces to a supplier worksheet.
Check mixed pitches before buying bundles ↓
This original, hypothetical example separates measurements, product coverage and whole-package purchasing. It is not a customer project, installation specification or current price quote.
Try the roof material planner →1. Count each roof face once
Assume a 50 × 30 ft building footprint, a simple symmetrical gable at 6:12, and no additional overhang beyond these entered dimensions. Split the horizontal projection into two 50 × 15 ft faces. Entering two 50 × 30 ft faces would double-count the roof.
Use plans or professionally supplied measurements; do not climb onto a roof for this example. If an outside overhang extends a face’s horizontal run by one foot, that face uses 50 × 16 ft before applying pitch. Add only the actual external extension, not another strip along the shared ridge. Triangular faces need their own projected base and perpendicular height.
2. Apply pitch to projection—not to a surface already measured
The 6:12 pitch factor is √(1 + (6 ÷ 12)²) ≈ 1.118034. Each horizontal 750 sq ft face becomes approximately 838.53 sq ft of roof surface. Together they cover 1,677.05 sq ft, or 16.77 roofing squares before allowance.
| Measurement | Calculation | Result |
|---|---|---|
| One projected face | 50 × 15 | 750 sq ft |
| One sloped face | 750 × √1.25 | 838.53 sq ft |
| Both faces | 2 × 750 × √1.25 | 1,677.05 sq ft |
| With 10% example allowance | 1,677.050983… × 1.10 | 1,844.76 sq ft |
Carry unrounded area into purchasing. If a supplier provides dimensions measured along each sloped face, choose “Measured sloped surface.” The pitch factor is then one; applying it again overstates the area. Different roof-face pitches must be entered separately.
3. Convert area into complete packages
For a hypothetical product with exactly 100 ÷ 3 sq ft per bundle, 1,844.756081… ÷ (100 ÷ 3) ≈ 55.34 bundles. Pooling the same compatible product across both faces means buying 56 bundles. Rounding each face separately also produces 28 + 28 = 56 in this example; other sizes can differ.
A second teaching product covers 25 sq ft per bundle, requiring 74 bundles. Do not assume “three bundles per square” fits every product. The exact installed package coverage controls the order, including differences between nominal and documented installed coverage.
4. Compare the whole purchase, not the bundle price
At a hypothetical $42 per bundle, the first product costs 56 × $42 = $2,352. At $34 per bundle, the second costs 74 × $34 = $2,516. Despite its cheaper bundle price, the second purchase is $164 higher. These prices are arithmetic teaching values, not current retail prices or recommendations that the products are interchangeable.
In the roof planner, leave optional accessories off, enter $42 and coverage 100 ÷ 3, then capture scenario A. Change coverage to 25 and price to $34. Compare equivalent warranties, installation requirements, taxes, delivery, accessories and labor before deciding.
5. Fill in accessories without guessing
Underlayment uses effective installed roll coverage after laps and required layers, not necessarily the roll’s printed gross area. Starter, hip/ridge cap and drip edge use separately entered installed lengths and effective package coverages. Roof surface area does not reveal these lengths or the correct installation system.
For illustration only, 1,677.05 sq ft plus 5% underlayment allowance at 900 effective sq ft per roll rounds to two rolls. Confirm the effective coverage and system requirements from the chosen instructions. Flashing, valleys, penetrations, fasteners, ventilation, tear-off, disposal, permits and structural repairs need separate evaluation or quotes.
Sources and limits
The geometry and quote comparisons above are original CalcCaddy calculations covered by regression tests. A roofing square is an area unit, not a bundle count. See GAF’s roofing-square explanation and the Owens Corning product-document library for exact product requirements.
No professional has certified this hypothetical roof. Confirm roof condition, structural capacity, pitch suitability, safe access and locally applicable requirements with qualified professionals. How CalcCaddy checks and corrects its work.
Build the full worksheet · Quick squares and bundles · Roof area methods