Roofing Calculator
Work out roofing squares, shingle bundles, underlayment and cost from your roof size and pitch.
Project Specifications
Material Estimates
A roof's true surface is always larger than its footprint on the ground, because the slope stretches it — and getting that right is the difference between ordering enough shingles and coming up short. This calculator takes the length and width of the roof plan, applies the pitch to find the real sloped area, and returns the number of roofing squares, shingle bundles, underlayment rolls, and nails you'll need, along with a full cost estimate. It even sketches the pitch angle. Everything runs in your browser.
Why pitch changes everything
Roof pitch is given as a rise in inches over a 12-inch run. The calculator converts that into a multiplier — the pitch factor — that scales the flat footprint up to the actual sloped area:
Pitch factor = √(1 + (rise ÷ 12)²) • Sloped area = Footprint × Pitch factor • Squares = Sloped area ÷ 100
A steeper roof has a larger factor and therefore more surface to cover. Roofing is measured in "squares," each equal to 100 square feet, which is how shingles and labour are quoted. So a 1,200 sq ft footprint at an 8:12 pitch becomes roughly 1,442 sq ft, or about 14.4 squares — noticeably more than the flat area would suggest.
Materials, waste and cost
Once it has the sloped area, the calculator adds your chosen waste percentage and works out the materials. Shingle bundles are figured from the coverage per bundle and rounded up; underlayment rolls include about ten percent for overlap; and nails are estimated at roughly 320 per square, then converted into whole boxes. The cost side multiplies each material by its unit price and adds labour, which is priced per square. All of this assumes a straightforward gable-style roof — complex roofs with many hips, valleys, and dormers generate more waste and cutting, so err toward the higher waste settings and confirm with a roofer for anything intricate.
Frequently Asked Questions
What is a roofing "square"?
A square is 100 square feet of roof area. Shingles, underlayment, and labour are all quoted per square, so the calculator converts your sloped area into squares as the common unit for ordering and pricing.
How do I find my roof pitch?
Pitch is the rise over a 12-inch horizontal run — a roof that climbs 6 inches per foot is a 6:12 pitch. You can measure it with a level and tape in the attic or on the roof edge, then select it in the calculator.
Why add a waste factor?
Cutting shingles to fit hips, valleys, edges, and penetrations always wastes some material. A waste allowance — often around ten to fifteen percent, more for complex roofs — ensures you order enough to finish the job.
Does it work for complex roofs?
It models a simple sloped roof accurately. For roofs with multiple hips, valleys, and dormers, the area and waste both rise, so use a higher waste setting and treat the result as a baseline to confirm with a contractor.
Is anything I enter saved?
No. The calculation runs in your browser and nothing you enter is uploaded or stored.