Estimate how many shingles (roofing squares) you need and the total cost to replace a roof, based on roof size, pitch, and shingle type.
| Roof area (footprint) | |
| Actual roof surface area | |
| Squares needed (incl. 10% waste) | |
| Estimated material cost | |
| Estimated labor cost |
Roofing is priced in "squares" — one square covers 100 square feet of actual roof surface. Because a sloped roof has more surface area than its flat footprint, a pitch multiplier is applied first.
The 1.10 factor adds 10% for waste from cuts, valleys, and overlaps — a standard estimating margin used by roofing contractors.
| Type | Cost per square |
|---|---|
| 3-tab asphalt | ~$100-150 |
| Architectural asphalt | ~$150-250 |
| Metal | ~$300-600 |
| Tile / slate | ~$400-1,000+ |
How much does it cost to replace a roof? For an average home (roughly 20-25 squares), total roof replacement typically runs from $8,000 for basic asphalt shingles to $25,000+ for metal or premium materials, including labor.
How many shingles do I need for my roof? Divide your roof's actual surface area (footprint × pitch multiplier) by 100 to get the number of squares, then add about 10% extra for waste from cuts and overlaps.
What's a roofing 'square'? A square is a roofing industry unit equal to 100 square feet of roof surface — shingles, underlayment, and labor are all typically priced per square.
Does roof pitch really affect the cost that much? Yes — steeper roofs have more actual surface area for the same footprint, plus they're slower and more dangerous to work on, both of which increase material and labor costs.
A sloped roof is larger than the flat footprint of the building underneath it. A 6/12 pitch rises 6 inches for every 12 inches of horizontal run, so its surface is about 1.118 times the footprint. Steeper roofs have larger multipliers, so they need more material and take more labour.
For example, a 40 ft × 30 ft footprint is 1,200 sq ft. With a 6/12 pitch the surface is roughly 1,341 sq ft, or about 13.4 roofing squares. Adding extra for waste raises the order to about 15 squares.
| Item | Notes |
|---|---|
| Tear-off and disposal | Removing and hauling away old roofing. |
| Underlayment and ice barrier | Protective layers under the shingles. |
| Flashing and vents | Seals around chimneys, valleys and pipes. |
| Ridge caps and starter strips | Finishing pieces along edges and peaks. |
| Labour | Often the largest share of the total cost. |
Why does the calculator add extra material? Cutting shingles around edges, hips and valleys creates offcuts, so a waste allowance prevents running short mid-project. Complex roofs need more.
Is the result a final price? No. It is an early estimate for planning. Labour rates, local building rules and roof condition change the real cost.