Roof area calculator: roof square footage and roofing squares from footprint and pitch

Multiply the roof's plan area, including the overhangs, by the slope factor for its pitch, √(rise² + 12²) ÷ 12. A 40 × 30 ft house with 12 in overhangs is a 42 × 32 ft plan of 1,344 sq ft; at 6/12 the factor is 1.1180, so the roof is 1,502.6 sq ft. Divide by 100 for squares, 15. The calculations work for gable, hip, shed and L-shaped roofs alike as long as every plane has the same pitch; where the pitch changes, compute each section and add them. The calculator does the arithmetic from either the footprint or a plan area, and prints the squares and edge lengths with it.

A roofing square is 100 sq ft of roof surface, the area of a 10 × 10 ft patch. It is the unit roofs are measured, ordered and quoted in, and it is always measured on the slope, not on the plan. To get squares, divide the roof area in square feet by 100: 1,502.6 sq ft is 15.03 squares. To go back, multiply by 100. Most 3-tab and laminated shingles come 3 bundles to the square, so a bundle covers about 33.3 sq ft; heavyweight and premium lines run 4 or 5 bundles per square, which is why the wrapper governs the bundle count and not the square. A square never covers 200 sq ft, whatever a label seems to say.

It depends on the stories and the pitch more than on the 2,000. A one-story 2,000 sq ft ranch, 50 × 40 ft with 12 in overhangs at 4/12, has 2,302.1 sq ft of roof, 23 squares and 25.3 to order at 10 % waste. The same 2,000 sq ft on two floors, a 40 × 25 ft footprint at 6/12, has 1,267.9 sq ft, only 12.7 squares. Add an attached garage or porch and those grow. That is why the house's living area is the wrong starting point: measure the outside walls, add the overhangs, enter the pitch, and the calculator gives the squares for that house.

A 20 × 20 ft garage with 12 in overhangs and a low 3/12 hip roof is 498.9 sq ft, about 5 squares, 5.5 to order and 17 bundles. A 24 × 24 ft garage with 12 in overhangs at 4/12 is 712.6 sq ft, 7.1 squares, 7.8 to order and 24 bundles, gable or hip. Answers to the same garage question often range from 5 to 7 squares because the pitch and the overhang were never stated; on the 20 × 20, a 2 ft overhang instead of 12 in adds about one square and 6/12 instead of 3/12 about 0.4 square, so measure both before ordering.

No. A regular hip roof has the same surface area as a gable over the same footprint at the same pitch, because every square foot of plan is tilted by the same angle under either roof. At the defaults both are 1,502.6 sq ft, and a 50 × 36 ft house is 2,209.2 sq ft either way; the hip's two trapezoids and two triangles add up to exactly that. A hip differs in other ways: about 15 % waste instead of 10 %, eaves on all four sides, 96 ft of hip cap on the default house, and hip and jack rafters. Any calculator that adds a hip adjustment to the area is double-counting the waste.

Measure the footprint from the ground and the pitch from inside. Walk the outside walls with a tape for the length and width, measure one overhang from the wall to the fascia, and read the pitch in the attic with a level and tape against a rafter, or at the gable rake with a speed square or a phone level held on a straightedge. From the plans, the roof plan or foundation plan plus overhangs gives the plan area directly. An online map tool can trace the plan outline from an aerial photo, but it measures plan area only, so multiply it by the slope factor. Climb only to check a plane you cannot see.

Yes. The shingles, underlayment and sheathing run to the edge of the overhang, so the plan area is measured to the outside of the fascia on every side. Add the eave overhang to both sides of the width and, on a gable, the rake overhang to both ends of the length; on a hip the eave overhang runs all round. On the default 40 × 30 ft house the 12 in overhangs add 1,344 sq ft − 1,200 = 144 sq ft of plan, 12 %. A 39 × 29 ft hip at 5/12 is 1,225.3 sq ft without its 18 in overhangs and 1,456 sq ft with them, about 2 squares apart, the usual reason two estimates disagree.

1.0541 for 4/12, 1.1180 for 6/12 and 1.4142 for 12/12, from √(rise² + 12²) ÷ 12. Multiply the plan area by it: 1,000 sq ft of plan is 1,054.1 sq ft of roof at 4/12, 1,118 sq ft at 6/12 and 1,414.2 sq ft at 12/12. Do not use 1.732 for 12/12; that is the hip and valley factor, √(rise² + 288) ÷ 12, which measures a hip rafter's length, and it overstates a 990 sq ft plan by about 3 squares. The multiplier table on this page lists every pitch from 1/12 to 18/12 with the roof area per 1,000 and 2,000 sq ft of plan.

Measure each section at its own pitch and add the sloped areas. Run the calculator for the main roof, then for each other section, and type the sloped figure from one run into the next as additional roof area, so the last run shows the total, the squares and the bundles. A gambrel has a steep lower slope and a shallow upper slope on each side: measure the plan width under each and run them separately rather than averaging the pitch. Dormers are small roofs of their own; a shed dormer is plan × its factor, a gable dormer the same. Valleys need no adjustment of their own, since they only mark where two planes meet.

Divide the roof's square footage by 100. The square footage must be the roof surface, not the floor area or the footprint: a 2,000 sq ft plan at 4/12 is 2,108.2 sq ft of roof and 21.1 squares, not 20. Then add waste to the unrounded squares, 23.2 at 10 %, and round only when you turn squares into bundles, 70 at 3 per square. If you already have a sloped area from an aerial report or a roofer's measurement, simply divide it by 100; do not type it into the calculator as the plan area, or the pitch will be applied twice.

About 10 % for a simple gable, 15 % for a hip or a cut-up gable and up to 20 % for a roof with many valleys, dormers or turrets. Those are trade rules of thumb, and the calculator's notes use the same figures; careful crews on simple roofs work under them. Waste is driven by the number of cuts, not by the steepness or the size, and it goes on the squares and bundles you buy, never on the measured area and never on the tear-off. On the default roof, 10 % turns 15 measured squares into 16.5 to order and 50 bundles; 15 % gives 17.3 and 52; 20 % gives 18 and 55.

Usually because of waste and accessories, not the area. Measured squares from careful work agree within a few percent; the gap opens when one party adds 8 % waste and another 15 %, when starter and cap are added as squares, or when the overhang or a porch roof is left out. A typical case: an adjuster's 2,849 sq ft plus 8 % is 3,077 sq ft, about 31 squares, while the roofer orders two more at 15 %. Ask each for the measured squares, the waste percentage and what is included, then compare like with like. A pitch read as 4/12 instead of 5/12 moves the area by 2.8 %.

Squares to order × bundles per square, rounded up: 50 for the default roof at 3 per square. Counts by shingle type are on the shingle calculator; the full method is in how to measure a roof for shingles.

Good enough to bid a job, not always to order one. Aerial roof measurement services and roof measuring apps build a model of each plane from imagery; one major shingle maker describes its own reports as generally about 95 % accurate, and that is the vendor's claim, not an independent test. The common errors are a pitch misread by half an inch per foot, overhangs hidden by trees or shadows, and porches or additions missed. A roof size calculator by address works the same way; this page has no address lookup, and free map tools give the plan outline only, with no pitch, so their figure must still be multiplied by the slope factor. Check any report's plan area against a tape on the outside walls, and its pitch against a level in the attic, before ordering.

The area is the same, but metal is ordered by panel length and count per run, not by squares. Use the metal roofing panel calculator (planned) for panels, screws and the R905.10.2 minimum slopes.

Measure the footprint and overhangs, read the pitch, and run this calculator for squares and edges; the step-by-step for shingles is in how to measure a roof for shingles.

Practically yes. A flat roof is never quite flat: built-up, modified bitumen and single-ply membrane roofs need a design slope of at least ¼ in per foot for drainage under the 2021 IRC, and at that slope the factor is 1.0002, so a 1,344 sq ft plan is 1,344.3 sq ft of roof. Measure the plan area to the outside of any parapet or edge, add the up-turns at walls and parapets separately if the membrane runs up them, and pick the flat shape in the calculator, which prints the perimeter for edge metal. A low-slope roof at 1/12 or 2/12 is not flat: use its pitch.

Read them from the edge rows. On the default 40 × 30 ft gable with 12 in overhangs at 6/12 there are 84 ft of eave, 71.6 ft of rake and a 42 ft ridge, so drip edge on eaves and rakes is 155.6 ft before laps, starter is 84 ft on the eaves or 155.6 ft if it also runs up the rakes, and ridge cap is 42 ft. The same house as a hip has 148 ft of eave and 106 ft of ridge and hip cap. Add laps and waste per the product, and turn the lengths into pieces and bundles on the shingle calculator.