Roofing Calculator

A simple gable is a footprint times a pitch factor. Enter the horizontal length and width and the rise per 12 of run, and the page returns squares and bundles. Three bundles per square is the usual asphalt packaging, and you can edit it. Hips, valleys, and a dormer cheek are extra area. Add waste or measure them as a second footprint rather than stretching this rectangle.

The slope factor is the only geometry that surprises people. A 6-in-12 pitch is a rise of 6 for a run of 12. The rafter length over that run is the hypotenuse, sqrt(12² + 6²) = sqrt(180), and the factor versus the flat run is sqrt(1 + 0.5²) = sqrt(1.25) = 1.11803. A 50 square metre footprint becomes 55.90 square metres. A flat roof has pitch 0 and a factor of 1, so the area equals the footprint. Steeper roofs grow quickly. A 12-in-12 pitch has a factor of sqrt(2), about 1.41. Enter the horizontal plan, which you can take from the wall plates, not a tape pulled along the shingle.

A square is a US roofing unit equal to 100 square feet. In metres that is 9.29 (100 sq ft).290304, from 0.09290304 square feet per square foot times 100. The example's 55.90 square metres is 6.02 squares. Bundles are that square count times the bundles in one square, rounded up. Three times 6.02 is 18.05, which rounds up to 19 bundles. Waste, if you set it, grows the area before the square conversion. Hips and valleys are not drawn as extra lines. A complicated roof needs either a higher waste percentage or several rectangles added together. Ridge caps, starters, and flashing are linear and are not in the bundle count.

Three bundles per square is labelled as usual asphalt packaging. Laminated and three-tab products sometimes differ, and a bundle can be sold as a different fraction of a square. Read the bundle and edit the field. Underlayment is the same kind of refusal as render coverage: the roll size is yours. A 10 square metre roll on 55.90 square metres is 6 rolls. Leave the field at 0 and the roll line stays 0. Do not borrow a roll size from another job.

Dormer roofs are extra area. The dormer calculator's triangular volume is not this surface. Measure the dormer roof as its own footprint and pitch, or add a waste allowance you can explain. Siding and exterior paint are the walls under the eaves, not the roof. There is no price per square and no labor rate.

Footprint length starts at 40 ft. Roof length in feet. Switch to m / cm for metres. Footprint width starts at 20 ft. Roof width in feet. Switch to m / cm for metres. Pitch starts at 6 rise / 12. Rise per 12 units of run. 6 means 6-in-12. A flat roof is 0 and the factor is 1. Waste allowance starts at 10 %. Hips, valleys, and starter courses waste more than a simple gable. The percentage is yours. Bundles per square starts at 3. Three is the usual number of bundles in a square of asphalt shingles. It is packaging, not a price. Edit it to the number printed on the bundle. Underlayment per roll starts at 400 sq ft. 400 sq ft is a typical roll of No. 15 asphalt felt (four roofing squares). Replace it with the figure on the roll you buy.

Ridges, hips, and valleys are measured in linear metres after the squares are known. A ridge cap is not a fraction of the bundle count unless the bundle maker says the same bundles include caps, which they usually do not. Starter strip along the eaves is another linear piece. If you have two different pitches, run the page once per pitch and add the bundles. A dormer cheek is wall, not roof, unless it is sloped. Round the bundle count up once. Do not round the squares up and also round the bundles up in a second pass beyond the ceil already in the formula.