Roof Square Footage Calculator

How to use this roof square footage calculator

Roof area is the surface you'd cover with shingles or metal. It's always more than the floor area of the house, because the roof hangs past the walls and because it's tilted. A roof square footage calculator corrects for both. Pick the tab that matches the information you have:

• House footprint. The quickest method. Measure the outside walls, add the overhang, pick the pitch. Best for a simple gable or hip roof with one pitch.
• Sections, mixed pitch. For houses where the garage, porch or an addition has a different slope from the main roof. Each section gets its own pitch, and the steep-roof charge is applied section by section.
• Roof planes. For when you can measure on the roof itself. Add each face as a rectangle, triangle or trapezoid. No pitch is needed for the area, because you measured the sloped surface directly.
• Satellite or records. Take a flat area from Google Earth, a county property record or a floor plan and convert it to roof area with the pitch.

Every method gives you roof square footage, square meters, roofing squares and an order quantity with waste. The breakdown table shows the math for each section, so you can check it.

How to calculate roof square footage

Plan area = (length + 2 × overhang) × (width + 2 × overhang)
Pitch factor = √(1 + (pitch ÷ 12)²)
Roof area = plan area × pitch factor
Squares = roof area ÷ 100
Order = squares × (1 + waste)

Worked example: a 50 by 28 ft house with 12-inch overhangs and a 6/12 roof.

• Plan area with overhangs: (50 + 2) × (28 + 2) = 52 × 30 = 1,560 sq ft.
• Pitch factor for 6/12: √(1 + 0.5²) = √1.25 = 1.118.
• Roof area: 1,560 × 1.118 = 1,744 sq ft, or 162 m².
• Squares: 1,744 ÷ 100 = 17.44 squares. With 10% waste, order about 19.2 squares.

The same formula works for gable, hip and shed roofs, as long as every face has the same pitch. A hip roof has the same area as a gable roof on the same house at the same pitch. It just needs more waste because of all the angled cuts.

Mixed pitches: the sections tab adds up each part separately. A 40 × 30 ft main roof at 6/12 is 1,200 × 1.118 = 1,341.6 sq ft. A 24 × 24 ft garage at 4/12 is 576 × 1.054 = 607.2 sq ft. A 20 × 8 ft porch at 3/12 is 160 × 1.031 = 164.9 sq ft. Total: 2,113.7 sq ft, or 21.14 squares.

How many squares is my roof?

A roofing square is 100 sq ft of roof surface. Roofers, suppliers and insurance adjusters all price roofs by the square, so it's the number to get right. Divide the roof area by 100. Then add waste for the material you cut off and throw away:

• 10% for a simple gable roof with long, straight runs.
• 15% for a hip roof, because every hip means angled cuts on both sides.
• 20% for a cut-up roof with valleys, dormers, skylights and short runs.

Most single-story US homes land somewhere between 15 and 30 squares. To turn squares into a shingle order with starter, cap, underlayment and nails, use our roofing shingles calculator. Most shingles come three bundles to a square.

Roof pitch factor table

Multiply the plan area by the factor. The last columns show the roof area for 1,000 and 2,000 sq ft of plan area, overhangs included.

Don't know your pitch? Measure it from the attic or the ground with our roof pitch calculator. If you have an angle in degrees or a percent grade, the roof slope calculator converts it.

Roof area calculator for hip roofs: triangles and trapezoids

When you can get on the roof, measuring each face is the most accurate method. Every face of an ordinary roof is one of three shapes:

• Rectangle: each side of a gable roof. Area = width × slope height.
• Triangle: the end of a hip roof. Area = width at the eave × slope height ÷ 2.
• Trapezoid: the long side of a hip roof, wide at the eave and narrow at the ridge. Area = (eave width + ridge width) ÷ 2 × slope height.

Measure slope height straight up the roof, at a right angle to the eave, not along a hip. For example, a 52 by 30 ft hip roof (overhangs included) at 6/12 has a 22-foot ridge and a slope height of 15 × 1.118 = 16.77 ft. The two trapezoids are (52 + 22) ÷ 2 × 16.77 = 620.5 sq ft each. The two triangles are 30 × 16.77 ÷ 2 = 251.6 sq ft each. Total: 1,744 sq ft, the same answer the footprint method gives. Those are the default rows on the "Roof planes" tab.

Planning a new roof? The rafter length calculator gives slope lengths, hips and ridge from the span and pitch.

Roof size from Google Earth or county records

You can get a good roof size without a ladder. In Google Earth, use the polygon measuring tool to trace the outline of the roof as seen from above. That outline already includes the eaves, so pick "Satellite" as the source. Multiply by the pitch factor and you have roof area. Trees and shadows can hide edges, so trace carefully and expect a few percent of error.

County property records and floor plans list area inside or along the outside walls, without the overhangs. They also often list total living area across every floor. For a roof you want the ground-floor footprint only, including the garage if it's under the main roof. Pick "County records" as the source and enter the building's perimeter and overhang. The calculator adds perimeter × overhang plus the four corners. For a 50 by 28 ft house, that's 156 × 1 + 4 × 1 = 160 sq ft, which brings 1,400 sq ft up to 1,560.

Roof cost per square foot by material

Once you know the roof area, the price follows. These are the typical US installed prices we use across FixHomeCost, per sq ft of roof surface:

• Asphalt shingles: $4 to $10 ($400 to $1,000 per square).
• Exposed-fastener metal: $7 to $15.
• Standing seam metal: $10 to $18.
• Tile or slate: $10 to $25.

Steep roofs cost more to work on. We add about 10% at 8/12 to 9/12, 20% at 10/12 to 12/12, and 30% above 12/12. In the sections tab that charge applies only to the steep parts of the roof. Low slopes limit what you can use: asphalt shingles aren't allowed below 2/12, and from 2/12 to 4/12 they need two layers of underlayment (IRC R905.2.2). The cost table flags materials that don't suit a section.

For a full replacement quote with tear-off and decking, use the roof replacement cost estimator or the metal roof cost calculator. For a patch, see roof repair cost per square foot.

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