Shingle Calculator

The short answer

Asphalt shingles are sold three bundles to the square, where one square covers 100 square feet of roof. A roof measuring 25 squares — 2,500 square feet — needs 75 bundles plus ridge and hip cap. Add 10 to 15% for waste, cutting and any future repairs, which on a roof this size is another 8 to 11 bundles.

What it depends on

Roof complexity changes the waste factor more than the area does. A simple gable wastes the least; hips, valleys, dormers and penetrations each add cuts, and a steep roof needs extra because courses are harder to keep straight and the exposure is harder to hold. Shingle type also matters — architectural laminates cover less per bundle than three-tab, and the bundle coverage is printed on the wrapper.

Where this stops being useful

This is a quantity estimate. Underlayment, ice and water shield, flashing, ventilation, deck condition and nailing pattern are all specified by manufacturer and code, and the number of layers already on the roof affects both the tear-off and the fastening. A roofing contractor can measure and specify the assembly. General information and planning only, not engineering, structural or code advice.

The waste allowance on a shingle roof is the largest in roofing, and it is not negotiable. Bundles are sized for a fixed area of coverage, but rows at the eaves, ridges and valleys all need cutting, and slopes with a break in them produce strips too short to use. A simple two-pitch roof generally needs about ten percent waste; a cut roof with valleys can need fifteen. Check the bundle's stated coverage rather than assuming, because shingle exposure varies by style and by how many tabs are visible per course.

Roofing quantities are usually the least scrutinised on a job and among the easiest to get wrong, because the waste shows up as a shortfall on the final rows rather than as a visible error. The result is a trip back to the merchant a day or two later, which costs more in time than the spare material would have cost in the first place.

Roof area is the input to several other decisions. Underlayment is measured in squares like the shingles themselves, and so is most of the accessory material. Starter strips along the eaves are measured by linear run, not area. If you are working out whether the structure can take the load, note that shingles add roughly three to four pounds per square foot, which is a meaningful addition on an older roof. Measure the actual dimensions rather than the plan, and check whether the roof needs to come off first — that changes the job from covering to tear-off and a full tear-off roughly doubles the labour.

Shingles are sold in bundles, three bundles usually cover one roofing square, and a square is one hundred square feet of finished roof. That chain of units is why a shingle order is quoted in squares rather than in bundles or in area: it is the language roofers and suppliers both use, and it hides a small amount of arithmetic that is easy to get wrong. Waste is the number that decides whether the order is right. A simple gable roof wastes the least, because most courses run unbroken from eaves to ridge. Hips, valleys, dormers, chimneys and skylights all force cuts, and the offcuts are rarely reusable. Ten per cent is a reasonable allowance for a straightforward roof; fifteen per cent or more is wiser for a complex one, and starter strips for the eaves and cap shingles for the ridges are extras on top of the field shingles. Materials beyond the shingles are easy to overlook when budgeting. Underlayment, drip edge, valley flashing, nails, and ridge and hip cap all belong in the order, and together they can add a noticeable share to the total. Underlayment in particular is measured in squares too, and its quantity generally matches the roof area with no waste, since it is laid in overlapping rolls. This calculator converts your roof area into squares and bundles, adds waste and rounds up, and estimates the ridge cap you will need along hips and ridges. It assumes three-tab or architectural shingles at the standard three bundles per square; some products differ, so check the coverage printed on the bundle before ordering.

This calculator returns estimates for planning and general information only. It is not engineering, architectural, structural, electrical or code advice, and it cannot replace a qualified professional who has seen the site. Material quantities depend on the actual dimensions, the product you buy and local building codes, so confirm the figures before ordering materials or starting work, and always follow local regulations.