Ordering shingles
A 40×30 ft house at 6/12 pitch has about 1,342 ft² of roof - roughly 13.4 squares, so order 15 to cover waste.
Roofing Calculator
Roofing - figures update as you type, nothing leaves your browser.
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A roofing calculator works out the true surface area of a roof - not just the footprint it covers, but the larger sloped area you actually have to shingle - from the building's length and width and the roof's pitch. It then converts that into roofing squares, the 100-square-foot unit shingles are sold and estimated in. The pitch matters enormously: a steep roof has far more surface than the flat outline beneath it, and ignoring that is the classic way to under-order materials and stall a job halfway through. The tool multiplies the footprint by a pitch factor derived from the rise-over-12 slope, which is how roofers convert a plan measurement into real roof area. A 6/12 pitch adds about 12% to the flat area; a 12/12 adds over 40%. Always add roughly 10% on top for waste, ridge caps, hips and valleys, and starter courses - the squares figure here is the net roof area, not the amount to buy.
Using Roofing Calculator
- Enter the roof's horizontal footprint dimensions in feet. Include the overhang in that footprint when it belongs to the area being covered; this is not necessarily the internal building size.
- Enter the rise for a run of 12, such as 6 for a 6/12 pitch. The calculator applies the slope multiplier to the footprint and divides the resulting area by 100 for roofing squares.
- Treat displayed squares as net surface area. Prepare separate quantities for starter strips, ridges, flashing and the waste allowance required by the selected material and roof layout.
Where roofing calculator helps
Before you use the result
- A 40 by 30 ft footprint at 6/12 pitch produces about 1342 square feet, or 13.42 roofing squares. The displayed area is rounded; keep enough precision when applying a material allowance before rounding to full bundles.
- One pitch value assumes the same slope across the measured footprint. Dormers, roof extensions and sections with different pitches need separate calculations. Do not count overlapping plan areas twice when combining them.
- A roofing square is 100 square feet, but the number of bundles per square depends on the product. Confirm coverage on the packaging. This estimate does not specify safe access, structural capacity, fastening patterns or local roof requirements.
Questions about Roofing Calculator
What is a roofing square?
100 square feet of roof surface. Shingles and estimates are quoted in squares, so converting your roof area to squares is how you order the right amount.
Is my data saved or uploaded?
No. Roofing Calculator calculates the result entirely in this browser; the values you enter are not stored or sent to a server.
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