Roofing Calculator
From the building’s size, overhang, pitch and roof type to the roof area, roofing squares and bundles of shingles to buy, with an optional installed cost.
Result
Buy 47 bundlesEstimate
Waste added, then rounded up to whole bundlesEvery rake, hip and valley leaves cut-offs, so the bundle count includes the allowance for the roof you picked.
- Roof surface area
- 1,408.72 ft² (130.87 m²)
- Roofing squares
- 14.09
- One square is 100 ft² of roof surface, before waste
- Squares with waste
- 15.5Estimate
- Footprint under the roof
- 1,260 ft² (117.06 m²)
- Slope factor
- 1.118
- Pitch angle
- 26.57 °
- Ridge length
- 42 ft (12.8 m)
https://calcgallery.com/roofing/roofing-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use the Roofing Calculator
- Pick where you are starting from. Most people know the house’s outside length and width; a footprint area or a sloped area from a roofer’s report works too.
- Add the eave overhang, then choose gable, hip, shed or gambrel and give the pitch as inches of rise per foot or in degrees.
- Choose the waste allowance that matches the roof. A hip, or any roof with valleys, needs the larger one.
- Read the bundles to buy, then the roof area and squares underneath. Open "More options" if your shingle wrapper lists a different bundle count per square.
- To see a rough job price, type a roofer’s price per square. A price per bundle totals the shingles alone.
How it is calculated
The roof is worked out from the plan, then converted to what the shingle trade sells:
footprint = (length + 2 × overhang) × (width + 2 × overhang)pitch factor = √(1 + (rise ÷ 12)²)roof area = footprint × pitch factorsquares = roof area ÷ 100 ft²bundles = ceil(squares × bundles per square × (1 + waste))A gable, hip or shed over the same plan at the same pitch has the same area; only the cutting differs. A gambrel mixes two pitches, so its factor is the steep lower slope’s factor and the shallow upper one’s, each weighted by the share of the span beneath it. If you start from a measured roof area, the pitch step is skipped entirely.
Metric users can enter the pitch in degrees instead: the factor is then 1 ÷ cos(angle). Squares stay at 100 ft², about 9.29 m², because bundles are packed against that unit even where metric is the norm.
The pitch multiplier at a glance
| Pitch | Angle | Multiplier |
|---|---|---|
| 3 in 12 | 14.0° | 1.031 |
| 4 in 12 | 18.4° | 1.054 |
| 5 in 12 | 22.6° | 1.083 |
| 6 in 12 | 26.6° | 1.118 |
| 8 in 12 | 33.7° | 1.202 |
| 10 in 12 | 39.8° | 1.302 |
| 12 in 12 | 45.0° | 1.414 |
Roofs between 4 and 8 in 12 add roughly a twentieth to a fifth over the flat plan. Above that the multiplier climbs quickly.
Practical tips
Measure the walls, not the roof. Run a tape along the outside of each wall at ground level, then measure how far the eave sticks out past the siding at one corner. A ladder at the gutter line gives the overhang more accurately than guessing from below. Rake overhangs at the gable ends are sometimes shorter than the eaves; if they differ a lot, split the difference.
Break an L-shaped or T-shaped house into rectangles. Work out each wing on its own and add the bundles, rather than drawing one big rectangle around the whole thing. Where wings meet you get valleys, so use the larger waste allowance for the job.
Garages, porches and dormers count. An attached garage with its own roof is another rectangle. Porch roofs are often a lower pitch than the house, so enter them separately with their own pitch. Dormer cheeks and small hips eat shingles out of proportion to their size.
Squares are for talking to suppliers and roofers. Quotes, delivery tickets and many product spec sheets are written in squares. Knowing yours lets you check a quote line by line rather than trusting a single total.
Shingles are only part of the order. Starter strip, ridge cap, underlayment, drip edge and flashing are sold separately and this page does not count them. Their quantities come from the eave, rake and ridge lengths and from the product you choose, so ask the supplier or check each product’s coverage label.
Buy one lot and keep a little back. Colour can shift between production runs, so order the whole roof at once. A leftover bundle or two stored flat makes future repairs match.
With your numbers
- Footprint = (length + 2 × overhang) × (width + 2 × overhang) = 1,260 ft²
- Slope factor = √(1 + (6 ÷ 12)²) = 1.118
- Roof area = 1,260 ft² × 1.118 = 1,408.72 ft²
- Squares = 1,408.72 ft² ÷ 100 ft² = 14.09
- Bundles = 14.09 × 3 per square × (1 + 10%) = 46.49, rounded up to 47
Quick reference
Every rake, hip and valley leaves cut-offs, so the bundle count includes the allowance for the roof you picked.
| Job | Shingle bundles to buy |
|---|---|
| 30 × 40 ft gable, 6 in 12, no overhang | 45 |
| 2,000 ft² footprint, 6 in 12 gable | 74 |
| 1,500 ft² house footprint, 4 in 12 gable | 53 |
| 40 × 28 ft hip roof, 6 in 12, 12 in overhang | 49 |
| 24 × 24 ft garage, 4 in 12, 12 in overhang | 24 |
| 30 × 50 ft ranch, 5 in 12, 12 in overhang | 60 |
| 12 × 10 ft shed roof, 3 in 12, 6 in overhang | 5 |
| 30 × 24 ft gambrel barn, 12 and 4 in 12 | 30 |
| 25 squares of roof, measured | 83 |
| 12 × 8.5 m house, 30° pitch, 30 cm overhang | 48 |
| 150 m² footprint, 6 in 12 gable | 60 |
Where the numbers come from
The fixed figures this calculator relies on, and the published source each one was checked against. How the calculators are built and checked
3 sources
Owens Corning, Supreme shingles, technical information: 3 bundles per square, https://www.owenscorning.com/en-us/roofing/shingles/supreme; GAF, "How Many Bundles of Shingles Are in a Square?" (2026): three for most 3-tab and architectural shingles, https://www.gaf.com/en-us/blog/your-home/how-many-bundles-of-shingles-are-in-a-square---63a47862-f7e1-4e73-abcf-8d09917a8b8d
Used for
- Bundles of asphalt shingles per roofing square (100 ft²). Three for three-tab and most architectural shingles; heavier premium and designer lines can take four to six.
Owens Corning, "DIY Roofing": add 10% to 15% for trim, https://www.owenscorning.com/en-us/roofing/blog/diy-roofing; IKO, "Estimating How Much Roofing Is Required", section D: 10% worked example, https://www.iko.com/na/wp-content/uploads/sites/8/document-library/Estimating-How-Much-Roofing-Is-Required.pdf
Used for
- Gable or shed roof allowance: 10% extra
Owens Corning, "DIY Roofing": add 10% to 15%, more for complicated roofs, https://www.owenscorning.com/en-us/roofing/blog/diy-roofing. 15% is the top of that range, for hips and valleys; no manufacturer states a hip-only figure
Used for
- Hip roof, or valleys allowance: 15% extra
Common questions about the Roofing Calculator
- How many bundles of shingles do I need for a 40 by 28 foot house?
- 47 bundles for a gable roof at 6 in 12 with a 12-inch overhang, at three bundles a square and a 10% gable allowance. The overhang makes the footprint 42 by 30 feet, 1,260 ft², and the pitch multiplier of 1.118 turns that into 1,408.72 ft² of roof, 14.09 squares. 14.09 × 3 × 1.1 = 46.49, rounded up to 47.
- How do I estimate a roof without climbing on it?
- Measure the house at ground level, add the overhang on each side, and multiply by the pitch multiplier. You can read the pitch from a gable end with a level and a tape, from the attic against a rafter, or from a photo taken square to the gable. Only the pitch needs a closer look; everything else comes off the walls.
- How many squares is a 2,000 square foot house?
- For a single-storey house, more than twenty: 2,000 ft² of floor becomes more roof once the slope and the eaves are counted. Choose "Footprint area", enter the ground area the roof covers including the overhang, and set the pitch. A two-storey house of 2,000 ft² sits under roughly half that footprint, so its roof is closer to half the size.
- Why does a hip roof need more shingles if the area is the same?
- A hip roof over a given footprint and pitch has the same surface as a gable, but every course that meets a hip is cut on an angle and the offcuts are small. Valleys add the same kind of cutting. That is why the hip choice carries a larger allowance, and a cut-up roof with dormers can justify more again.
- What does roofing cost per square?
- It depends on the product, the tear-off, the roof’s steepness, access and where you live, so this page holds no price data. Enter the per-square figure from a written quote to see a total. The page multiplies it by the squares including waste, so ask the roofer whether their price is per measured square or per square ordered.
- When should I call a roofer instead?
- Call one before buying if the roof is steep, over one storey, or has soft spots, sagging, leaks or rot, since the answer there may be decking repairs before any shingles. Roofers also know what underlayment, ice barrier and ventilation your area expects. Local codes vary, and some places require a permit or limit how many layers a roof may carry.