Roofing Calculator
Estimate roof area, squares, shingle bundles, and cost.
Estimate roofing materials
Material estimate
Whole field-coverage bundles
- Roof area before waste
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- Area including waste
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- Roofing squares (including waste)
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- Bundle cost
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Simple rectangular gable roof. Enter the horizontal area the roof covers including overhang — a typical eave and rake overhang adds around 15% to the footprint, more than a 10% waste allowance covers. Accessories, hips, valleys, and complex planes are excluded.
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How to use the roofing calculator
Enter the building footprint length and width, roof rise for every 12 inches of horizontal run, a waste allowance, and the actual coverage and price of one bundle. The result estimates sloped surface area, roofing squares, whole bundles, and field-material cost.
Formula and assumptions
For a simple symmetrical gable roof, the combined horizontal area of both planes equals the rectangle you enter, so enter the horizontal area the roof covers including any overhang. The slope factor is the square root of 1 + (rise ÷ 12)². Roof area equals that rectangle multiplied by the slope factor.
This model assumes one uniform pitch and adds waste to the entire calculated area. Bundle count always rounds up after dividing by the entered manufacturer coverage. The roofing-squares figure shown with the result includes the waste allowance, so it is the material to buy rather than the measured roof surface.
Important limitations
Enter the horizontal roof projection, not the wall dimensions. Overhangs are part of the roof: a 40 by 30 foot building with an 18-inch eave and 12-inch rake overhang projects 42 by 33 feet, about 15 percent more area than the footprint — more than a 10 percent waste allowance absorbs.
Real roofs may also contain hips, valleys, dormers, intersecting sections, unequal planes, curved surfaces, or multiple pitches. Measure each plane or use verified plans for ordering. Field bundles do not include ridge caps, starter courses, underlayment, flashing, drip edge, ventilation, nails, or disposal. Re-roofing usually requires a permit, and tear-off, the number of existing layers, and deck condition all affect what may legally be installed.
Roof work presents serious fall and weather risks. Do not climb or measure a roof without suitable training, equipment, conditions, and fall protection. Confirm quantities, permits, local code, structural requirements, and product instructions with qualified professionals and suppliers.
Frequently asked questions
What is a roofing square?
One roofing square is 100 square feet of roof surface, not 100 square feet of building footprint.
How does roof pitch change the estimate?
The calculator multiplies horizontal footprint area by the slope factor derived from rise over a 12-inch run.
Does bundle coverage always equal one-third of a square?
No. Coverage varies by product, exposure, shingle style, and packaging. Use the coverage printed by the manufacturer.
Does this include ridge caps or starter shingles?
No. The bundle count models field coverage only. Ridge, hip, starter, flashing, underlayment, valleys, and fasteners require separate takeoffs.