How the roofing estimate calculator is calculated
roof area = (length + 2 × overhang) × (width + 2 × overhang) × pitch factor
squares = area ÷ 100, rounded to 2 places; order = squares × (1 + waste), up to a third of a square
price = (order × material + squares × (labor + tear-off) + flat costs) × (1 + markup)
Worked example: a 40 by 30 ft house, 6/12 pitch
These are the example defaults loaded above: a 1 ft overhang, 10% waste, $120 of material, $90 of labor and $35 of tear-off per square, $450 of flat costs and a 20% markup.
| Line | Amount |
|---|---|
| Footprint, 42 x 32 ft with overhang | 1,344 sq ft |
| Pitch factor at 6/12 | 1.118 |
| Roof area, 1,344 x 1.118 | 1,502.6 sq ft |
| Squares | 15.03 |
| Order with 10% waste (to a third) | 16.67 |
| Material, 16.67 x $120 | $2,000.00 |
| Labor, 15.03 x $90 | $1,352.70 |
| Tear-off, 15.03 x $35 | $526.05 |
| Dumpster, permit, other | $450.00 |
| Cost to you | $4,328.75 |
| Markup at 20% | $865.75 |
| Job price | $5,194.50 |
Every default in the calculator is an example so you can see a result straight away. None is a market average. Replace each with your own costs and rates.
Why pitch changes the area
A roof is bigger than the footprint of the building under it, and the steeper it is the bigger the difference. The pitch factor is the length of the slope for each foot of run. At 6/12 it is 1.118, so a 1,344 sq ft footprint carries about 1,503 sq ft of roof.
Squares and waste
Roofing is sold by the square, 100 sq ft. Shingles overlap and get cut at hips, valleys and edges, so you order more than the measured area. The waste allowance is your call: a plain gable needs less than a roof with many valleys.
Measure from the roof when you can
This works from the building footprint, which is a good first number for a quote. Dormers, a second level and attached garages need their own pass, and a site visit should confirm the final figure before you commit to a price.
Turn this into an estimate or invoice
The button under the result carries these lines into the document generator, ready to edit. To price the whole job section by section with waste and a deposit, open the cost estimator set up for roofing. For roofing designs and presets, see the roofing invoice page.
Related calculators
- Contractor invoice calculatorLabor, materials and job costs into an invoice
- Markup calculatorTurn markup into margin and back
Questions people ask
How do I calculate roof area from the footprint?
Multiply the footprint, including any overhang, by the pitch factor. The factor is the square root of 1 plus the rise over 12, squared.
What is a roofing square?
One square covers 100 square feet of roof. Material and labor are commonly priced per square.
How much waste should I allow?
It depends on the roof. Plain gables need less; roofs with many hips and valleys need more. Enter the percentage you use.
Is tear-off included?
Only if you enter a tear-off price per square. Set it to 0 when you are not removing old roofing.
Are the defaults typical roofing prices?
No. They are examples so the calculator shows a working result. Replace each one with your own costs.
How do I turn this into a quote?
Use the button under the result to carry the material, labor, tear-off and markup lines into a quote, estimate or invoice.