Footprint versus roof surface
The most common roofing estimate mistake is pricing the footprint instead of the surface. A satellite measurement, a floor plan or a tape measure around the eaves gives you the horizontal area. The actual roof is bigger because it slopes, and the steeper it is the bigger the difference: 5% at 4/12, 12% at 6/12, 25% at 9/12 and 41% at 12/12. Leave the "area is the footprint" option on and the calculator applies the multiplier for the pitch you pick. If you measured the slopes directly, or your measurement report already gives roof surface, turn it off.
Pitch is written as rise over run: 6/12 means the roof rises 6 inches for every 12 inches horizontally. The multiplier is the length of the slope for a 12-inch run, which is the hypotenuse of that triangle divided by 12. Roofs with more than one pitch should be measured section by section and added together.
Waste, bundles and what to order
Every roof needs more material than its surface area: shingles are cut at edges, hips, valleys and around penetrations, and starter and ridge courses add their own. Ten percent covers a straightforward gable roof; fifteen percent is safer with hips and valleys, and complex roofs with many dormers can run twenty. Shingles come three bundles to the square, so the calculator rounds the waste-adjusted figure up to the next third of a square and prices materials on that. Labor and tear-off are priced on the installed squares, without waste, because crews are paid for the roof, not the offcuts.
Setting your cost inputs
- Materials per square: shingles plus underlayment, ice and water shield, drip edge, nails, ridge cap and flashing, divided by the squares they cover. Architectural shingles alone are often $100 to $150 a square; a full material package is more.
- Labor per square: what you pay the crew per installed square, including the time for flashing and detail work. Steep or cut-up roofs cost more per square than simple ones.
- Tear-off per square: removing the old roof. Set it to zero for new construction or an overlay, and raise it for two or more existing layers.
- Permits and disposal: flat amounts for the job. Disposal includes the dumpster and tipping fees, which scale with the weight of the tear-off.
- Overhead: the share of direct cost that covers your office, insurance, trucks, tools and marketing. Many roofing companies run 10 to 20%.
- Profit: applied on top of cost and overhead. The calculator treats it as a markup; if you think in margin, remember that a 20% markup is a 16.7% margin.
Reading the price per square
Roofers compare bids per square because it normalises for roof size. The calculator gives the all-in price per installed square and per square foot of roof surface, so you can sanity-check a bid against jobs you have done and against what competitors charge in your area. If the number looks low, the usual reasons are a missing tear-off, waste set to zero, or overhead left out. If it looks high, check that the pitch multiplier is not being applied twice: once in your measurement report and again here.
For other parts of the business, the markup calculator and profit margin calculator show how markup and margin relate, and the break-even calculator tells you how many jobs a month cover your overhead.
What the calculator does not include
It prices shingle roofs by the square and does not account for metal panels, tile or flat membrane systems, which are usually priced by the linear foot or by the sheet. It does not add sales tax, financing fees or warranty reserves, and it does not estimate decking replacement, which is best quoted as a per-sheet allowance in the contract. Use the result as the starting point for your proposal and add those items as separate lines.