Roofing Squares Explained: From Footprint to Bundles

What is a roofing square?

One roofing square is 100 sq ft (9.29 m²) of roof surface. It is a convenient unit because most asphalt shingles are packaged so that three bundles cover one square. A 2,000 sq ft roof is 20 squares, or about 60 bundles before waste.

Step 1: measure the footprint

Measure the outline of the roof as seen from above, including the eaves and rake overhangs — not the walls of the house. For a simple rectangular house with 1 ft overhangs and 40 × 28 ft walls, the footprint is 42 × 30 = 1,260 sq ft. Complex roofs can be broken into rectangles. Plans or satellite measurement services can help; avoid climbing on the roof just to measure.

Step 2: apply the pitch factor

Pitch is the rise in inches per 12 in of horizontal run. The pitch factor converts footprint to sloped area: factor = √(1 + (rise ÷ 12)²).

For the 1,260 sq ft footprint at 6/12: 1,260 × 1.118 = 1,409 sq ft, or 14.1 squares.

Step 3: add waste

Cuts at hips, valleys, rakes and around chimneys and vents create waste. A simple gable roof usually needs about 10% extra; a hip roof or a roof with dormers and valleys needs 15% or more. Our example gable roof: 14.1 × 1.10 = 15.5 squares → 47 bundles at three per square.

Accessories

• Starter strip along the eaves and often the rakes — measured in linear feet.
• Ridge cap shingles along ridges and hips — sold by linear coverage per bundle.
• Underlayment over the whole deck, with overlaps; synthetic rolls cover more area than felt.
• Ice and water barrier at eaves and valleys in cold climates, as required by code.
• Drip edge, flashing and nails.

Bundles per square vary

Most three-tab and standard architectural shingles are three bundles per square, but heavier designer shingles may be four or five. Always check the wrapper. Our roofing calculator lets you change bundles per square.

Worked example: a hip roof

1. House 36 × 24 ft with 1.5 ft overhangs: footprint 39 × 27 = 1,053 sq ft.
2. Pitch 8/12: factor 1.202 → 1,053 × 1.202 = 1,266 sq ft = 12.7 squares.
3. Hip roof waste 15%: 12.7 × 1.15 = 14.6 squares.
4. Three bundles per square: 14.6 × 3 = 43.7 → 44 bundles.
5. Ridge and hips: one ridge of 12 ft plus four hips of about 21 ft each ≈ 96 ft of ridge cap.

Hip length depends on pitch and plan size; measuring on site or from plans is more reliable than estimating, and a roofer will confirm it during a quote.

Underlayment and tear-off

Underlayment covers the whole roof deck. Synthetic underlayment rolls commonly cover 4–10 squares each, while traditional #15 felt rolls cover about 4 squares and #30 about 2 squares, with overlaps reducing effective coverage. If you are replacing a roof, budget for tearing off and disposing of the old shingles — dumpster size depends on the number of squares and layers, and many areas limit how many layers can stay on the roof.

Getting a roofing quote

Even if you hire a roofer, knowing the number of squares helps you compare quotes. Ask each contractor for the number of squares they measured, the waste factor they used, the shingle line, underlayment type, whether tear-off and disposal are included, and how they will handle any rotten decking found during tear-off (usually priced per sheet). Quotes that differ widely in squares for the same house deserve a question — one may have missed a section, or the other may be padding the waste.

In metric markets, tiled and slate roofs are priced per square meter and by the number of tiles per m² at a given gauge. The same footprint × pitch factor method gives the roof area; the tile manufacturer's data gives the count per m².

• Squares and pitch measured
• Waste factor and shingle line
• Underlayment, ice barrier and flashing included?
• Tear-off, disposal and decking repairs
• Warranty terms for materials and labor

Low-slope roofs

Asphalt shingles are designed for sloped roofs. Most manufacturers require a minimum slope of 2/12, with special double-layer underlayment between 2/12 and 4/12. Below that, a low-slope membrane system is used instead, and it is measured in squares the same way but priced and installed differently. If part of your roof — a porch or a dormer — is close to flat, measure it separately so it is not counted as shingle area.

Safety

Roof work is one of the most dangerous DIY tasks. Use fall protection, never work alone or in wet or windy weather, and consider hiring a licensed roofer for steep pitches.