Roofing Calculator
- Materials
- Labor
- Tear-off
- Profit
Ridge cap, starter strip and drip edge are bought by the linear foot; add them to other materials.
Turn this into a quote
A one-page PDF for your customer, filled in from the numbers above. Your markup isn't shown.
How the roofing calculation works
Measure the footprint, overhangs included
Length × width of the building plus eaves and rakes. A 40 × 30 ft footprint is 1,200 sq ft.
Multiply by the pitch factor
The factor is √(12² + rise²) ÷ 12. A 6/12 roof is 1.118, so 1,200 sq ft of footprint is about 1,342 sq ft of roof.
Add waste and convert to squares
One roofing square is 100 sq ft. With 10% waste, 1,342 sq ft becomes 14.76 squares.
Bundles = squares × bundles per square
Most shingles come 3 bundles to a square. Round up: 14.76 × 3 = 44.3, so order 45 bundles.
Add tear-off for each old layer
Removing one layer at $75 a square on 13.42 squares of roof is $1,006.23, including disposal. Two layers double it.
Price it: materials + labor + tear-off, then markup
Add crew hours at your cost per hour and the tear-off, then apply your markup. A 30% markup on cost is a 23% margin on the price. Divide by the roof's squares for the price per square.
Worked example. A 40 × 30 ft roof at 6/12 pitch is 1,342 sq ft of roof. With 10% waste that is 14.76 squares, or 45 bundles at $42 = $1,890. Add $600 of other materials, 48 labor hours at $55 ($2,640) and tearing off one old layer at $75 a square ($1,006.23) for a cost of $6,136.23. A 30% markup prices the roof replacement at $7,977.10, or $594.58 per square of roof. Without tear-off it's $6,669.
Roofing FAQ
How many squares is my roof?
Multiply the footprint by the pitch factor, add waste, and divide by 100. A 1,200 sq ft footprint at 6/12 with 10% waste is 14.76 squares.
How many bundles of shingles are in a square?
Usually three bundles cover one square (100 sq ft). Some heavy designer shingles need four or five, so check the wrapper before you order.
How do I calculate roof square footage from the ground?
Measure the house footprint including overhangs, then multiply by the pitch factor for your slope. You don't need to climb the roof for an estimate.
How much waste should I add for roofing?
About 10% for a plain gable roof and 15–20% for hip roofs or roofs with many valleys and dormers, because more shingles get cut.
How do roofers price a roof replacement?
Most price per square: materials plus crew labor, then a markup to cover overhead and profit. Tear-off, disposal and permits are often added as separate lines.
How much does it cost to replace a roof?
It depends on the roof's size and pitch, the shingles or other material, how many old layers come off, and your local labor costs. Enter your numbers above for the full price and the price per square.
What is the roofing cost per square?
The full job price divided by the roof area in squares (100 sq ft each, before waste). The calculator shows it so you can compare quotes or check your own pricing.
How much does roof tear-off add?
Each old layer you remove adds crew time and disposal for every square of roof. Enter your tear-off cost per square and the number of layers; two layers cost about twice as much to remove.