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Calculation details
Planning estimate only. Verify dimensions, waste, coverage, product specifications, and local requirements before purchasing materials.
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What does this calculator estimate?
A 40 x 25 ft roof at 6-in-12 pitch works out to about 1,118 sq ft of roof area, or roughly 1,230 sq ft once a 10% waste allowance is added. That is about 12.3 roofing squares, which is roughly 37 bundles at three bundles per square. Check your own pitch and material coverage in the BoringToolsKit roofing calculator before you order.
- Roof area is footprint area times a pitch factor; a 6-in-12 pitch multiplies a flat footprint by about 1.12. (Source: BoringToolsKit calculation methodology)
- Roofing material sells by the square, which covers 100 sq ft, so 1,230 sq ft is about 12.3 squares. (Source: BoringToolsKit calculation methodology)
- The 10% waste allowance is a starting point and rises with valleys, hips and cuts in the roof. (Source: BoringToolsKit calculation methodology)
How this calculator works
Formula
roof area = footprint area × pitch factor; bundles/squares depend on material coverage
Worked example
A 40 x 25 ft roof with a 6-in-12 pitch: pitch factor 1.12 gives 1,118 sq ft of roof, 1,230 sq ft with 10% waste, about 12.3 roofing squares or 37 bundles.
Assumptions to verify
- Pitch factor is approximate
- Waste varies with valleys/hips/cuts
- Roof safety/pro inspection may be required
Frequently asked questions
What is a roofing square?
A roofing square is 100 square feet of roof area.
Should I rely on this for ordering shingles?
Use it for planning only. Roof shape, pitch, waste, and local codes should be verified.
Cite this tool
BoringToolsKit. “Roofing Calculator.” boringtoolskit.com/roofing-calculator/. Free to reference in articles, syllabi, and answer posts with a link.
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