Convert a roof's footprint area into actual sloped surface area and roofing squares, then apply your own price per square. Pitch factor is trigonometry; the rate comes from your quote.
| Input | Result |
|---|---|
| 2,000 ft² footprint, 6:12 pitch, $500/square, 10% waste | 1.118× pitch factor · 24.6 squares · $12298.37 |
| 1,500 ft² footprint, 4:12 pitch, $450/square, 12% waste | 1.054× pitch factor · 17.71 squares · $7968.94 |
| 3,000 ft² footprint, 12:12 pitch, $600/square, 15% waste | 1.414× pitch factor · 48.79 squares · $29274.22 |
The most common estimating mistake is pricing a roof from the building’s floor area. The roof is inclined, so its true surface is the plan area multiplied by the pitch factor, the hypotenuse of a 12-inch run and your rise, expressed as a multiplier. At 4:12 the factor is about 1.054; at 12:12 it is 1.414, meaning a 45° roof has roughly forty percent more surface than the floor beneath it.
Roofers price in squares, 100 square feet of finished roof, which is also how shingles are bundled. Working in squares is what lets a quote be compared apples to apples between contractors.
What is not in this arithmetic: the material choice, the number of existing layers to strip, roof complexity, and local labour. All four move the price substantially and none can be derived from an area, so they come from your written quote. Get two or three before committing.
A square is 100 square feet of finished roof, the unit roofers quote in and the unit shingles are packaged against. Three bundles of standard architectural shingles cover roughly one square. Quoting in squares is why the first thing any roofer does is convert your footprint to squares.
Because a pitched roof is a set of inclined planes, and the incline is longer than its horizontal projection. The factor is the hypotenuse of a right triangle whose run is 12 and whose rise is your pitch, divided by 12. At 6:12 that factor is about 1.118, so a 2,000 ft² footprint is about 2,236 ft² of actual roof surface, you buy material for the slope, not the plan.
It varies with material, roof complexity, how many layers have to be torn off, and local labour rates, enough that any single national figure would mislead most readers. Get two or three written quotes for your specific roof and enter the per-square rate from the one you intend to use.
Yes, normally ten percent, and more for complex roofs. Valleys, hips, dormers and chimneys all generate cuts, and starter courses and ridge caps are bought separately from the field shingles.
Only if your per-square rate includes it. Many roofers quote removal of existing layers as a separate line item, so check whether the rate you entered covers the full job or just the new material.