Measure roof area, then order by product coverage
For a simple rectangular gable or equal-pitch hip roof. This tool connects a plan measurement and pitch to purchase quantities; it does not replace a field takeoff for a complex roof.
Formula and worked example
Roof area = (length + 2 × overhang/12) × (width + 2 × overhang/12) × √(1 + (pitch/12)²). Squares = roof area ÷ 100. Bundles = round up(order area ÷ 100 × bundles per square).
A hypothetical 40 × 24 ft building with 12 in overhang on every side has a 42 × 26 ft roof plan. At 6/12 pitch its sloped area is about 1,220.89 ft². With 10% allowance and three bundles per square, the purchase estimate is 41 bundles. At 400 ft² usable coverage per roll, it needs four underlayment rolls. Bundle and roll yields depend on the selected products.
Start with the horizontal roof footprint
Enter the building's length and width, then the overhang on each side in inches. The calculator adds twice the overhang to both dimensions, creating a horizontal roof footprint. This is different from measuring the sloped surface itself. If your measurements already include the full roof edges, set overhang to zero rather than adding it to a footprint that already contains it.
A roof with different overhangs on different sides cannot be represented exactly by one uniform overhang field. Calculate an appropriate full footprint outside this tool or break the job into sections. Confirm the basis of each measurement before comparing two estimates: a building footprint, eave-to-eave plan and measured roof surface are three different quantities that can produce different answers.
Read pitch as rise over twelve inches of run
A 6/12 pitch means six inches of vertical rise for twelve inches of horizontal run. The pitch slider changes the illustrated height and the calculated slope multiplier together. The angle is the arctangent of rise divided by twelve. A 0/12 entry produces a flat mathematical area, but that result does not establish whether a shingle product or roof system is suitable for that slope.
The slope factor multiplies the horizontal plan area by the square root of one plus the pitch ratio squared. At 6/12, the ratio is 0.5 and the multiplier is approximately 1.118. A steeper pitch increases sloped area for the same horizontal footprint. It can also affect labor and access costs, which must be entered separately rather than assumed to follow the same area multiplier.
Use the simple gable and hip assumptions correctly
The gable view has two roof planes meeting at a ridge. The hip view uses four planes with the same pitch over a rectangular plan. For this simple equal-pitch model, the area factor is the same even though the edge layout differs. The hip mode requires length to be at least width so the modeled ridge can run along the longer dimension without a negative length.
Complex hips, unequal pitches, valleys, dormers and intersecting additions need their own measurements. This tool does not infer those features from the shape selector. Neither view selects framing members or details roof loading. Treat the wireframe as a way to understand the stated measurement assumptions, then use actual roof sections and product requirements for a complete material list.
Convert area into squares and whole bundles
A roofing square is a unit of area equal to 100 square feet. It is not one package of shingles. The calculator first reports net squares from the sloped area, then applies the order allowance and your entered bundles-per-square yield. Three bundles per square is an example starting value; the actual package coverage varies by product and must be checked before ordering.
Bundle purchases round upward after the area and allowance are combined. Do not round the net squares upward first and then multiply by bundles, which can overstate the purchase count unnecessarily. Conversely, do not assume that an area-only quantity covers the layout waste from cuts, hips or valleys. The allowance is editable because waste depends on the selected material and actual roof geometry.
Estimate usable underlayment coverage and accessories
Enter the usable coverage of one roll after the overlap and installation requirements for your product. The starting 400 square feet is a hypothetical input, not a universal roll size. The purchase count divides the roof's allowance-adjusted area by that net coverage and rounds up. It does not add starter, ice-barrier zones or other extra layers that have a different coverage basis.
Underlayment, flashing and other accessory costs belong in their separate dollar allowance. Include delivery and other material charges when applicable, and avoid counting costs already included in a bundle quote. Ridge caps, starter strips, fasteners, edge materials and ventilation components are not automatically quantified by this roof-area model. Keep a separate product checklist with the estimate so an apparently complete bundle count does not hide missing accessories.
Price the installation and review what is excluded
The material total is whole bundles multiplied by your bundle price plus the accessory allowance. The prep, labor and other-cost input should account for the work you are quoting, such as tear-off, disposal, equipment, protection, cleanup and overhead. Changing pitch updates area and bundles immediately, but it does not automatically estimate the additional crew time or access equipment required for a steep roof.
Choose a target margin only after the complete cost estimate is entered. Copy the bid summary or transfer it to the estimate studio to document the scope. Compare the result with your actual completed jobs and local supplier quotes. A quantity calculation is useful evidence for pricing, but it does not establish a market rate, customer acceptance or the suitability of a roofing system.
Frequently asked questions
Is a roofing square the same as a square foot?
No. One roofing square is 100 square feet of roof area. A 1,200 square foot roof is twelve net squares before any order allowance. Bundle quantities then depend on the product's coverage.
Why do gable and simple hip roofs show the same area?
For the same rectangular footprint and a uniform pitch on every plane, the slope multiplier applies to the whole plan. Edge lengths and cutting requirements differ. This model does not treat that equal area as equal labor or equal accessory demand.
Does the calculator include shingles for valleys and ridges?
It estimates field-shingle bundles using your allowance. It does not separately quantify ridge caps, starter, valley materials or penetration details. Include those in a separate product takeoff and the accessory-cost allowance.