How Many Squares of Shingles Do I Need?

What a roofing square is

Shingles are sold and quoted in squares. One square covers 100 square feet of roof surface. A bundle is a fraction of a square, and most common shingles come at 3 bundles per square. So the question "how many shingles do I need" is really two questions: how many square feet of roof do I have, and how much extra should I allow for cutting and waste.

Step 1: measure the footprint

You do not need to climb onto the roof to estimate it. Measure the outside length and width of the house at the walls. For an L-shaped or T-shaped house, split it into rectangles and measure each one. Garages and porches with their own roofs are separate sections.

Step 2: add the overhang

The roof extends past the walls at the eaves and rakes. Measure how far the roof edge sticks out, often around 12 inches, and add it to every side. A 40 by 30 foot house with a 1 foot overhang has a roof footprint of 42 by 32 feet, which is 1,344 square feet instead of 1,200.

Step 3: find the pitch

Pitch is written as rise over a run of 12, such as 6/12. You can measure it in the attic with a level and tape, or from the edge of the roof with a pitch gauge. The roof pitch calculator converts a rise and run, or an angle, into the pitch and the multiplier you need.

Step 4: apply the pitch multiplier

A sloped roof is longer than the flat footprint under it. The multiplier is √(1 + (rise ÷ 12)²). Multiply the footprint by it to get the roof surface.

The multiplier works for gable and hip roofs alike, as long as all the planes share the same pitch.

Step 5: add waste and convert to squares

Every roof loses some material to cuts at edges, hips and valleys. Add the allowance, then divide by 100 to get squares. Multiply by bundles per square and round up.

Worked example

The 40 by 30 foot house with a 1 foot overhang and a 6/12 roof:

1. Footprint with overhang: 42 × 32 = 1,344 ft².
2. Roof surface: 1,344 × 1.1180 = 1,502.64 ft².
3. With 10% waste: 1,652.9 ft², or 16.53 squares.
4. Bundles at 3 per square: 16.53 × 3 = 49.59, so 50 bundles.

A larger example: a 50 by 26 foot house with a 1 foot overhang, an 8/12 roof and 15 percent waste comes to 1,749.89 ft² of roof, 20.12 squares and 61 bundles. With underlayment rolls that cover 400 ft² each, it needs 6 rolls.

How much waste to allow

Items that are not part of the bundle count

• Starter strip along eaves and often rakes, counted by linear foot.
• Ridge cap along ridges and hips, usually a separate product.
• Underlayment and ice and water shield, counted by roll coverage.
• Drip edge, flashing, vents and nails.

The eave and rake perimeter from the calculator is a good starting point for drip edge and starter strip, since both run along the roof edge.

Measuring an L-shaped or complex roof

Most houses are not a single rectangle. Split the footprint into rectangles that each have one roof over them, work out each one, and add the results. For example, a main house of 40 by 28 feet and a wing of 16 by 14 feet, both with a 1 foot overhang and a 6/12 roof:

• Main roof: 42 × 30 = 1,260 ft² of footprint × 1.1180 = 1,408.7 ft².
• Wing: 18 × 16 = 288 ft² × 1.1180 = 322.0 ft². Where the wing meets the main roof, the overlapping overhang is counted twice, which works as a small extra allowance.
• Total: 1,730.7 ft². With 15 percent waste for the valley, 1,990.3 ft², or 19.9 squares and 60 bundles.

If a porch or garage has a different pitch, use its own multiplier instead of the main one.

Ridge cap, starter and edge materials

These are counted by length, not area:

• Ridge cap: measure every ridge and, on a hip roof, every hip. The coverage per bundle of ridge cap is printed on the package in linear feet.
• Starter strip: runs along the eaves and, with many products, up the rakes. The eave and rake perimeter from the calculator is a good first figure.
• Drip edge: usually sold in 10 foot pieces. Divide the perimeter by 10 and round up, adding a piece or two for overlaps and corners.
• Ice and water shield: often required along eaves and in valleys in cold climates. Check your local code for how far up the roof it must run.

Underlayment

Synthetic underlayment and felt are sold in rolls with a stated coverage. Divide your roof surface with allowance by that coverage and round up. On the 50 by 26 foot example, 2,012 ft² with 15 percent allowance needs 6 rolls that cover 400 ft² each. Roll coverage often already accounts for the side lap, so check the label.

Before you order: a short checklist

• Confirm bundles per square on the exact shingle you are buying.
• Order shingles from the same production lot so the color matches across the roof.
• Count ridge cap, starter strip, drip edge, underlayment and nails as separate lines.
• Ask whether unopened bundles can be returned, and keep one or two for future repairs.
• Check that the roof deck is sound before new shingles go on; damaged sheathing is a separate cost.

Turning squares into a budget

Shingle prices vary a lot by product and region, so the calculator does not assume any. Ask your supplier for a price per bundle, enter it, and you get the shingle cost for your exact bundle count. Then add the separate lines above, plus tear-off, disposal and labor if you are hiring a roofer. Comparing two quotes is easier when you know your own square count: if one quote is based on many more squares than your measurement, ask how they measured.

Common mistakes

• Using the floor area of the house instead of the roof footprint with overhang.
• Forgetting the pitch multiplier, which undercounts steep roofs by 20 percent or more.
• Counting a porch or garage roof at the main roof pitch when it is flatter or steeper.
• Assuming every shingle uses 3 bundles per square without checking the wrapper.

Frequently asked questions

How many squares is a 2,000 square foot house?

It depends on the footprint, not the living area. A two-story house of 2,000 square feet may have a 1,000 square foot footprint. At a 6/12 pitch with a modest overhang and 10 percent waste, that is roughly 13 to 14 squares. Run your own numbers in the roofing calculator.

Is a hip roof bigger than a gable roof?

At the same pitch and footprint, the roof surface is the same. A hip roof usually needs more waste allowance and more ridge cap because of the hips.

Can I install shingles on a low-slope roof?

Most asphalt shingle makers set a minimum pitch, often 2/12 with extra underlayment and 4/12 for standard installation. Check the product instructions.