How to Calculate Roof Squares
By the Calculator.hair team · Updated · 6 min read
Short answer
One roofing square is 100 square feet of roof surface. To find your squares, multiply the footprint in square feet by the pitch multiplier, √(12² + rise²) ÷ 12, then divide by 100. An 1,800-square-foot footprint at a 6/12 pitch is 1,800 × 1.118 = 2,012 square feet, or 20.12 squares, before overhangs and waste.
Key takeaways
- One roofing square covers 100 square feet, an area equal to 10 feet by 10 feet.
- Pitch multiplier = √(12² + rise²) ÷ 12, so a 6/12 roof has 1.118 times the area of its footprint.
- Many standard shingles come in three bundles per square, but heavier laminated products can take four or five, so check the wrapper.
- Waste depends on the roof: published figures range from about 1% on a simple roof to 15% on a cut-up one.
How many feet are in a roof square?
A roof square is 100 square feet, an area equal to a 10 × 10-foot patch of roof. Roofers and suppliers use it so they can quote materials in smaller numbers: a 2,200-square-foot roof is 22 squares.
A square measures the sloped surface of the roof, not the floor below. A roof is always bigger than its footprint, because it slopes and usually overhangs the walls. That is the most common error in a home estimate: a 1,800-square-foot footprint does not mean 18 squares of roof.
How do you calculate squares on a roof?
Find the area of each roof plane in square feet, add them together, and divide by 100. A plane is one flat sloped section of the roof, and its area is its width along the eave times its length from eave to ridge.
Worked example: a simple gable roof has two identical planes, each 44 feet long and 20 feet from eave to ridge. Each plane is 44 × 20 = 880 square feet, the two total 1,760 square feet, and 1,760 ÷ 100 = 17.6 squares. Our square footage calculator handles rectangles and triangles if you are working through several planes.
Measuring on the roof gives the best number, but climbing up carries a real fall risk. If you would rather stay on the ground, estimate from the footprint and pitch instead, as shown below, and have a roofer measure before you order.
What is the roof pitch multiplier?
The pitch multiplier is the factor that converts a flat footprint area into sloped roof area: √(12² + rise²) ÷ 12. Pitch is written as rise over run, so a 6/12 roof rises 6 inches for every 12 inches of horizontal run. The square root is the Pythagorean theorem at work, since rise and run form the legs of a right triangle and the roof surface is the hypotenuse. See triangle formulas for more on that.
For a 6/12 pitch, √(144 + 36) = √180 = 13.416, and 13.416 ÷ 12 = 1.118. For a 9/12 pitch, √(144 + 81) = √225 = 15, and 15 ÷ 12 = 1.25.
The table shows each multiplier, with the area and squares for a 1,500-square-foot footprint and no overhang, as our roofing calculator computes them.
| Pitch | √(12² + rise²) | Multiplier | Angle | Roof area from 1,500 sq ft | Squares |
|---|---|---|---|---|---|
| 2/12 | √148 = 12.166 | 1.0138 | 9.5° | 1,521 sq ft | 15.21 |
| 3/12 | √153 = 12.369 | 1.0308 | 14° | 1,546 sq ft | 15.46 |
| 4/12 | √160 = 12.649 | 1.0541 | 18.4° | 1,581 sq ft | 15.81 |
| 5/12 | √169 = 13 | 1.0833 | 22.6° | 1,625 sq ft | 16.25 |
| 6/12 | √180 = 13.416 | 1.118 | 26.6° | 1,677 sq ft | 16.77 |
| 7/12 | √193 = 13.892 | 1.1577 | 30.3° | 1,737 sq ft | 17.37 |
| 8/12 | √208 = 14.422 | 1.2019 | 33.7° | 1,803 sq ft | 18.03 |
| 9/12 | √225 = 15 | 1.25 | 36.9° | 1,875 sq ft | 18.75 |
| 10/12 | √244 = 15.620 | 1.3017 | 39.8° | 1,953 sq ft | 19.53 |
| 11/12 | √265 = 16.279 | 1.3566 | 42.5° | 2,035 sq ft | 20.35 |
| 12/12 | √288 = 16.971 | 1.4142 | 45° | 2,121 sq ft | 21.21 |
How many squares is my roof?
Multiply the footprint, including overhangs, by the pitch multiplier and divide by 100. The footprint is the flat area the roof covers when seen from directly above. Because the multiplier depends only on the slope, it works for a gable or hip roof as long as every plane has the same pitch. If the planes differ, calculate each one separately.
Worked example: a house with an 1,800-square-foot footprint, a 6/12 pitch and a 1-foot overhang. Without the overhang, the roof is 1,800 × 1.118 = 2,012 square feet, or 20.12 squares. The roofing calculator adds the overhang by treating the footprint as a square: √1,800 is about 42.43 feet per side, adding 1 foot on each side gives 44.43 feet, and 44.43² is about 1,974 square feet. Multiplying by 1.118 gives 2,207 square feet, or 22.07 squares.
That square shape is a simplification. A long, narrow house has more perimeter than a square one with the same floor area, so its overhangs add more roof. Dormers, garages and additions at a different pitch also need their own calculation. Treat a footprint-based figure as an estimate for budgeting, not an order quantity.
How many bundles of shingles are in a square?
Three bundles per square is the most common packaging, so each bundle covers about 33.3 square feet. It is not universal. According to Fine Homebuilding, three bundles applies to most three-tab strip shingles and some lightweight laminated shingles, while heavier three-tab and laminated shingles can take four or sometimes five. GAF gives an example within its own range: its Timberline HDZ line is three bundles per square and its Woodland line is four.
Bundles = squares × bundles per square, rounded up. Always read the coverage on the wrapper or the product's data sheet, because that is the number that applies to your shingle.
How do you calculate shingles for a roof with waste?
Multiply the squares by 1 plus your waste allowance, then by bundles per square, and round up. For the 22.07-square roof above at three bundles per square, that is 67 bundles with no waste, 73 with 10%, and 77 with 15%, the figures our roofing calculator returns.
Sources disagree on the allowance, and no single figure fits every roof. Many estimating guides use 10% to 15%, which is what our calculator displays. A Fine Homebuilding estimating article is much lower: its author figures about 1% for a simple roof and adds 5% or sometimes more for a complex roof with open valleys, and counts starter and cap shingles separately. Treat all of these as rules of thumb. Waste rises with every hip, valley, dormer and chimney, so a roofer's takeoff for your actual roof should win over any percentage.
The table covers three- and four-bundle products. The three-bundle rows come from our calculator, and the four-bundle rows are our own arithmetic on the same 22.07 squares.
| Waste allowance | Squares | Bundles at 3 per square | Bundles at 4 per square |
|---|---|---|---|
| None | 22.07 | 67 | 89 |
| 10% | 24.28 | 73 | 98 |
| 15% | 25.38 | 77 | 102 |
What is not included in a shingle count?
A count based on area covers the main field of the roof, and several items along the edges and ridges need separate figures.
- Starter shingles along the eaves and rakes, unless your count already allows for them.
- Hip and ridge cap shingles, which are often sold as a separate product.
- Underlayment, ice barrier where required, drip edge, flashing, vents and nails.
- Tear-off and disposal of the old roof, if it is being replaced.
Calculators in this guide
Frequently asked questions
How many square feet are in a square of shingles?
A square of shingles covers 100 square feet of roof. At three bundles per square, each bundle covers about 33.3 square feet.
How many squares is a 2,000-square-foot roof?
A roof with 2,000 square feet of actual surface is 20 squares. If 2,000 square feet is the house's footprint, multiply by the pitch multiplier first, so a 6/12 pitch with no overhang gives about 22.36 squares.
How do I find my roof pitch?
Measure how many inches the roof rises over 12 inches of horizontal run, using a level and a tape. A 6-inch rise makes a 6/12 pitch, and the roof's plans may also list it.
How many bundles of shingles do I need for 20 squares?
At three bundles per square, 20 squares needs 60 bundles before waste, and 66 with a 10% allowance. Heavier four-bundle shingles need 80 before waste.
Does a steeper roof need more shingles?
Yes. A steeper roof has more surface over the same footprint, so a 12/12 roof has about 1.41 times the footprint's area, while a 4/12 roof has about 1.05 times.