Estimate pitched roof surface area, bundles or packs needed, roofing squares, and material cost for common roofing projects.
This roofing calculator is an estimate only. Actual roof quantities depend on eaves, rakes, hips, valleys, dormers, underlayment, ridge accessories, overlap requirements, and manufacturer coverage rates. Confirm final quantities with your roofer or supplier.
freeusukcalculator.com
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A roof has more surface area than the building footprint beneath it because of its slope. The calculator works out the flat footprint, then multiplies by a pitch factor that accounts for the steepness. A steeper roof has a larger pitch factor β a 6:12 pitch adds about 12% to the flat area, while a 12:12 pitch adds roughly 41%.
Roofers measure in squares, where one square equals 100 square feet of roof surface. Materials like shingles are sold and estimated by the square, so converting your total area into squares makes ordering straightforward.
Once you know the number of squares, you can estimate shingles, underlayment and fasteners. Most asphalt shingles cover one square per three bundles, plus extra for starter strips and ridge caps. Underlayment, drip edge and flashing are estimated from the roof perimeter and valleys.
Add a waste factor of 10β15% β toward the higher end for complex roofs with many hips, valleys and dormers, which require more cutting. Buying a little extra from the same batch also gives you matching spares for future repairs. For steep or high roofs, factor professional installation into your budget, as the labour and safety requirements rise sharply with pitch.
Find the flat footprint area, then multiply by a pitch factor to account for the slope, since a pitched roof has more surface than the ground it covers. The calculator applies the pitch multiplier for you.
A "square" is the roofing industry unit equal to 100 square feet of roof area. Materials like shingles are sold and estimated by the square, so the calculator converts your area into squares.
A steeper pitch increases the actual roof surface for the same footprint, so it needs more material. A 6:12 pitch, for example, adds about 12% to the flat area.
Add roughly 10-15% for waste from cuts, ridges, valleys and hips. Complex roofs with many angles need the higher end of that range.