Roofing Calculator
Estimates only. Check bundles per square and coverage on your product's label, and measure complex roofs plane by plane.
A roofing square is 100 square feet, and most shingles come three bundles to the square, so a 2,000 sq ft roof is 20 squares or 60 bundles before waste. Roof area isn't house area, though: a 40 × 30 ft house with a 1 ft overhang and a 6/12 pitch has about 1,503 sq ft of roof, which is 16.5 squares or 50 bundles with 10% waste. Enter your house size and pitch below for squares, bundles, underlayment, starter, ridge cap, and drip edge.
Bundles of shingles by roof area
| Roof area | Squares | Bundles (no waste) | +10% (gable) | +15% (hip) |
|---|---|---|---|---|
| 1,000 sq ft | 10 | 30 | 33 | 35 |
| 1,200 sq ft | 12 | 36 | 40 | 42 |
| 1,500 sq ft | 15 | 45 | 50 | 52 |
| 1,800 sq ft | 18 | 54 | 60 | 63 |
| 2,000 sq ft | 20 | 60 | 66 | 69 |
| 2,500 sq ft | 25 | 75 | 83 | 87 |
| 3,000 sq ft | 30 | 90 | 99 | 104 |
How to calculate roof area with pitch
Roof area is not the same as house area. Start with the footprint of the house plus the overhang on every side, then multiply by the pitch factor, which is how much longer a sloped surface is than its flat footprint: pitch factor = √(1 + (rise ÷ 12)²). A 6/12 roof has a factor of 1.118, so it is about 12% bigger than its footprint; a 12/12 roof is about 41% bigger. The roof pitch calculator gives the factor for any pitch.
The useful shortcut is that a gable roof and a hip roof over the same footprint, at the same pitch, have exactly the same area. The hip roof just slopes on four sides instead of two. What changes is the edges: a gable has a long ridge and four sloped rakes, a hip has a short ridge and four hips. That is why the roof type only changes the waste and the trim, not the square count.
Worked example: a 40 × 30 ft house
With a 1 ft overhang the footprint is 42 × 32 ft, or 1,344 sq ft. At a 6/12 pitch that becomes 1,344 × 1.118 = 1,503 sq ft of roof, or 15.0 squares. Add 10% for a gable roof and you need 16.5 squares, which is 50 bundles at three bundles per square. The same house with a hip roof has the same area but takes 15% waste, or 52 bundles, plus 106 ft of hip and ridge cap instead of 42 ft of ridge.
Roofs with dormers, valleys, or several pitches
Split the roof into planes, work out each plane's area (its footprint × its own pitch factor), and add them up. Then use the Measured roof area option and enter the total. Valleys and dormers add cuts, so use the hip-roof waste or more.
How many bundles of shingles do I need?
Shingles are sold by the square, which is 100 square feet of roof, and packed in bundles. Standard three-tab and most architectural shingles come three bundles to the square, but not all: Owens Corning's Duration Premium line takes four bundles per square and its Woodcrest line six. Check the bundles-per-square figure on your shingle's label and enter it above.
Owens Corning advises adding 10% to your material totals for trim and waste, which suits a simple gable roof. Hip roofs, valleys, and dormers need more cut shingles, so the hip preset uses 15%. Round up to whole bundles at the end, not square by square. The table above shows the bundle count for common roof sizes, and the FAQ covers a few typical houses and garages.
The rest of the roofing materials list
- Underlayment. It covers the whole roof deck under the shingles. A synthetic roll such as Owens Corning ProArmor is sold as 10 squares and covers 929 sq ft once the 3-inch overlaps are taken out, which is the default above. Felt rolls cover far less per roll, so enter the coverage from your roll's label.
- Starter strip. A row of starter shingles runs along the eaves and up the rake edges so the first course is sealed down. Owens Corning Starter Strip Plus covers about 105 linear feet per bundle.
- Ridge and hip cap. The cap shingles cover the ridge and every hip. Coverage per bundle differs a lot between products, so the calculator gives the length to cover; enter your bundle's coverage to turn it into bundles.
- Drip edge. Metal drip edge runs along the eaves and rakes and is sold in 10 ft pieces; overlapping the pieces is why it is worth rounding up.
- Ice barrier. Where your local code designates a risk of ice dams, the International Residential Code requires an ice barrier from the eave edge to at least 24 inches inside the exterior wall line (IRC R905.1.2). That strip is extra to the underlayment above.
How much does it cost to shingle a roof?
Enter a price per square above and the calculator multiplies it by your squares with waste and gives a cost per square foot. HomeGuide puts an installed asphalt shingle roof at about $3 to $5 per square foot.
| Shingle | Materials per square | Installed per square |
|---|---|---|
| 3-tab | $80–$130 | $200–$500 |
| Architectural / dimensional | $100–$250 | $400–$600 |
| Luxury / premium | $150–$280 | $500–$700 |
Roof types and materials
- Gable roof. The default: two slopes, a full-length ridge, and four sloped rake edges that take starter and drip edge.
- Hip roof. Slopes on all four sides, so the eaves run all the way around and there are no rakes. Expect more waste and more cap shingles for the hips.
- Shed and low-slope roofs. Asphalt shingles are allowed only on slopes of 2/12 or steeper, and from 2/12 up to 4/12 the code calls for a double layer of underlayment (IRC R905.2.2). Below 2/12, use a low-slope membrane instead of shingles.
- Metal roofing. The roof area and squares here apply to metal too. Panels are counted differently: divide the eave length by the panel's coverage width for the number of runs, and use the rafter length for the panel length.
Common mistakes
- Using the house's square footage. A two-story 2,000 sq ft house may have only a 1,000 sq ft footprint, while a steep roof adds area. Measure the footprint and apply the pitch factor.
- Forgetting the overhang. A 1 ft overhang adds 144 sq ft to a 40 × 30 ft house before pitch.
- Assuming three bundles per square. Heavier designer shingles can take four or more. Use the number on your bundle.
- Leaving trim off the list. Starter, cap, drip edge, and underlayment are separate purchases that a bare bundle count leaves out.
What this calculator can't handle
- Complex roofs. Dormers, turrets, and roofs with several pitches need plane-by-plane measuring; add the planes and enter the total area.
- Tear-off and decking. Removing old layers and replacing damaged sheathing are separate costs and materials.
- Flashing and vents. Step flashing at walls, chimney flashing, valley metal, and ridge vents are not counted.
- Local code. Ice barrier, underlayment, and wind requirements vary by area; check with your building department.
About these figures: the square (100 sq ft), bundles per square, and the 10% allowance follow Owens Corning's product specifications and guidance, and the underlayment and starter coverage are Owens Corning ProArmor and Starter Strip Plus figures. The slope and ice-barrier rules are from the International Residential Code, section R905. Costs are from HomeGuide's asphalt shingle cost guide. The 15% hip-roof waste is common practice rather than a published standard, so adjust it to your roof.
Frequently asked questions
How many bundles of shingles are in a square?
Most shingles come three bundles to the square, and a square covers 100 sq ft of roof. Some heavier lines differ: Owens Corning Duration Premium takes four bundles per square and Woodcrest six, so check the bundles-per-square figure on your shingle's label.
How many bundles of shingles do I need for 1,000 sq ft?
1,000 sq ft of roof is 10 squares, or 30 bundles at three per square. With 10% waste for a gable roof that is 33 bundles; with 15% for a hip roof, 35. Make sure the 1,000 sq ft is roof area, not the house's floor area.
How many squares of shingles do I need for a 2,000 sq ft house?
It depends on the footprint and the pitch, not the floor area. A one-story 2,000 sq ft house has about 2,000 sq ft of footprint; with a 1 ft overhang and a 6/12 pitch that is roughly 2,440 sq ft of roof (for a 50 × 40 ft footprint), or about 27 squares with 10% waste. A two-story house of the same floor area has half the footprint and about half the roof.
How do I calculate roof area with pitch?
Multiply the footprint, including the overhang, by the pitch factor √(1 + (rise ÷ 12)²). The factor is 1.054 for a 4/12 roof, 1.118 for 6/12, 1.202 for 8/12, and 1.414 for 12/12. Gable and hip roofs of the same pitch over the same footprint have the same area.
How many squares of shingles do I need for a 24 × 24 garage?
A 24 × 24 ft garage with a 1 ft overhang and a 4/12 roof has about 713 sq ft of roof, or 7.1 squares. With 10% waste that is 7.8 squares, or 24 bundles at three per square.
How much roofing underlayment do I need?
Enough to cover the whole roof area. A 10-square synthetic roll such as Owens Corning ProArmor covers 929 sq ft after its 3-inch overlaps, so a 1,500 sq ft roof needs two rolls. Felt rolls cover much less per roll; use the coverage printed on the roll.
How many bundles of starter strip and ridge cap do I need?
Starter runs along the eaves and rakes: a 40 × 30 ft gable house with a 1 ft overhang has about 156 ft of edge, or two bundles at 105 ft per bundle (Owens Corning Starter Strip Plus). Ridge cap covers the ridge plus any hips; divide that length by the coverage printed on your cap bundle.
What waste factor should I use for roofing?
Use about 10% for a simple gable roof, as Owens Corning recommends for trim, and about 15% for hip roofs and roofs with valleys or dormers, which need more cut shingles. The waste goes on the squares before you round up to bundles.
How much does it cost to shingle a roof?
An installed asphalt shingle roof costs about $3 to $5 per square foot, according to HomeGuide: $200 to $500 per square for 3-tab and $400 to $600 for architectural shingles. The shingles alone run about $80 to $250 per square. Enter your price per square in the calculator for a total and a cost per square foot.
What is the minimum roof pitch for asphalt shingles?
The International Residential Code allows asphalt shingles on slopes of 2/12 or steeper (R905.2.2). From 2/12 up to 4/12 it requires a double layer of underlayment. Flatter roofs need a low-slope membrane instead of shingles.
Related calculators
Sources
- Supreme 3-Tab Shingles — product specificationsOwens CorningThree bundles per square for three-tab shingles; other Owens Corning lines differ (Duration Premium four, Woodcrest six). A square is 100 sq ft of roof.
- ProArmor Synthetic Roof UnderlaymentOwens Corning10-square roll, 286 ft × 42 in, covering 929 sq ft with a 3-in. overlap.
- Starter Strip Plus ShingleOwens CorningOne bundle provides about 105 linear feet of starter coverage.
- International Residential Code, Chapter 9: Roof Assemblies (R905)International Code CouncilR905.2.2: asphalt shingles on slopes of 2:12 or greater, double underlayment from 2:12 up to 4:12. R905.1.2: ice barrier from the eave edge to at least 24 in. inside the exterior wall line where required.
- How Much Does an Asphalt Shingle Roof Cost?HomeGuideInstalled cost of $3–$5 per sq ft; per square $200–$500 (3-tab) and $400–$600 (architectural) installed, $80–$250 materials only. November 2025.