Roofing Calculator
Free roofing calculator for shingle roofs. Enter your house footprint and pitch, or the roof area, to get roofing squares and how many bundles to buy.
- Free, no signup
- Formula shown
- Rounds up to whole units
- Updated October 2026
Shingle bundles · 10% allowance
51bundles
Roofing squares
16.53
with allowance
Roof area
1,503 sq ft
15.03 squares
- Footprint incl. overhangs
- 1,344 sq ft
- Slope factor (6/12)
- 1.118
- Area with allowance
- 1,653 sq ft
Uniform-pitch roofs only. Ridge cap, starter strip, flashing, and drip edge are not included.
AnswerA 40 × 30 ft footprint with 1 ft overhangs and a 6/12 pitch has about 1,503 sq ft of roof (15.03 squares); with a 10% allowance that is 16.53 squares, so buy 51 bundles of shingles at 32.8 sq ft per bundle.
How to use this roofing calculator
- Choose feet or meters, then pick Footprint + pitch or, if you already know it, Roof area.
- Enter the house length and width measured at the walls, and the overhang that extends past each wall at the eaves and rakes.
- Enter the pitch as rise per 12 of run. If you don't know it, measure it with the roof pitch calculator.
- Enter the coverage per bundle printed on the shingle wrapper, or tap one of the published product figures.
- Set a waste allowance for cuts at hips, valleys, and rakes, and optionally your underlayment roll coverage.
How to calculate roofing squares: the formula, shown
Roofing is ordered by the square, which is 100 square feet of roof area. A roof is larger than the footprint it covers because it slopes. For roof planes that all share one pitch, the sloped area is the plan area (including overhangs) times the slope factor √(1 + (pitch ÷ 12)²). That holds for a simple gable roof and for a hip roof whose planes share the same pitch.
Default example. A 40 × 30 ft footprint with 1 ft of overhang on every side, a 6/12 pitch, a 10% allowance, and 32.8 sq ft per bundle. That coverage is the figure Owens Corning publishes for TruDefinition Duration shingles (98.4 sq ft per 3-bundle square); it is an example input only. Change the inputs above and the result panel recalculates; this worked example always shows the default.
Plan area = (40 + 2 × 1) × (30 + 2 × 1) = 42 × 32 = 1,344 ft² Slope factor = √(1 + (6 ÷ 12)²) = 1.118 Roof area = 1,344 × 1.118 = 1,502.64 ft² Squares = 1,502.64 ÷ 100 = 15.026 squares Allowance = 1,502.64 × (1 + 10/100) = 1,652.9 ft² (16.529 squares) Bundles = 1,652.9 ÷ 32.8 ft²/bundle = 50.393 → 51 bundles
The bundle count divides by the coverage printed on the wrapper rather than assuming 3 bundles per square, because coverage per bundle differs between products.
Roofing squares for common house sizes
Roofing squares for common rectangular footprints with 1 ft of overhang on every side, computed with the same formula as the calculator. There is no waste allowance in these figures.
| Footprint | 4/12 pitch | 6/12 pitch | 8/12 pitch | 12/12 pitch |
|---|---|---|---|---|
| 36 × 24 ft | 10.41 | 11.05 | 11.87 | 13.97 |
| 40 × 30 ft | 14.17 | 15.03 | 16.15 | 19.01 |
| 50 × 40 ft | 23.02 | 24.42 | 26.25 | 30.89 |
| 60 × 40 ft | 27.45 | 29.11 | 31.3 | 36.83 |
| 60 × 50 ft | 33.98 | 36.05 | 38.75 | 45.59 |
Slope factors used: 4/12 = 1.054, 6/12 = 1.118, 8/12 = 1.202, 12/12 = 1.414. Find your pitch with the roof pitch calculator.
How many bundles of shingles to buy
For the default roof, buy 51 bundles at 32.8 sq ft per bundle: 16.53 squares including the 10% allowance.
- Field shingles only: the count covers the roof surface. Ridge cap, hip cap, and starter strip are separate products with their own coverage, so measure ridges, hips, and eaves in linear feet and check those products' labels.
- Underlayment: enter the coverage from the roll label to count rolls. Overlap requirements are set by the product's installation instructions.
- Complex roofs: dormers, multiple pitches, and intersecting roofs need each plane measured separately. Add the plane areas and use Roof area mode. Raise the allowance for many valleys and hips.
- Specifications: this is a quantity estimate. Minimum slopes, underlayment type, ventilation, and fastening come from the shingle manufacturer's instructions and local code.
Shingle calculator: coverage per bundle by product
IKO notes that the key figure is the area covered per bundle, and that not every shingle is packaged three bundles to a square. These published figures show why the calculator asks for coverage instead of assuming it:
| Product | Coverage per bundle | Bundles per 100 sq ft | Manufacturer packaging |
|---|---|---|---|
| Owens Corning TruDefinition Duration | 32.8 sq ft | 3.05 | 3 bundles cover 98.4 sq ft |
| IKO Cambridge | 33.3 sq ft | 3 | 3 bundles per square |
| IKO Armourshake | 20 sq ft | 5 | 5 bundles per square |
Bundles per 100 sq ft = 100 ÷ coverage per bundle, before rounding up and before allowance. Use the figure on your own wrapper.
Roofing squares calculator
Squares are roof area ÷ 100. The result panel shows squares before and after your allowance so you can compare with a contractor's quote, which is usually priced per square.
Tips for measuring a roof
- Measure the footprint on the ground: it is safer than measuring on the roof, and the slope factor converts it to roof area.
- Include the overhang. On a small house, a 1 ft overhang on every side adds noticeable area.
- Measure each roof section separately when wings of the house have different pitches, then add the areas.
- Count bundles from the wrapper of the exact product and color you are buying, and keep a spare for repairs.
- Work on a roof only with proper fall protection. Hire a professional if you are not equipped to do it safely.
Roofing calculator FAQ
How do I calculate how many squares my roof is?
A roofing square is 100 square feet of roof area. Multiply the footprint including overhangs by the slope factor for your pitch to get the roof area, then divide by 100. For a 6/12 pitch the slope factor is about 1.118.
How many squares is a 30 x 40 house roof?
With 1 ft of overhang on every side and a 6/12 pitch, the footprint is 42 × 32 ft and the roof is about 1,503 sq ft, or 15.03 squares before any waste allowance. A steeper or shallower pitch changes the answer.
How many bundles of shingles are in a square?
It depends on the product. IKO says most popular shingles are packaged so three bundles cover a square, but some need more: its Armourshake covers 20 sq ft per bundle, or five bundles per square. Owens Corning lists 98.4 sq ft per 3-bundle square for TruDefinition Duration. Check the coverage on your wrapper.
How many bundles of shingles do I need?
Divide the roof area plus your waste allowance by the coverage per bundle on the wrapper and round up. For the default 40 × 30 ft house at 6/12 with a 10% allowance and 32.8 sq ft per bundle, that is 51 bundles.
Does roof pitch change how many shingles I need?
Yes. A steeper roof has more surface over the same footprint. The slope factor is 1.054 at 4/12, 1.118 at 6/12, 1.202 at 8/12, and 1.414 at 12/12.
How much extra shingle should I buy for waste?
There is no single figure. Simple gable roofs need less than roofs with many hips, valleys, and dormers, where more shingles are cut. The calculator uses a 10% allowance as an adjustable example; raise it for complicated roofs.
Does this include ridge cap, starter strip, or underlayment?
Ridge cap and starter strip are not included; they are separate products measured in linear feet. Underlayment rolls are counted only if you enter the roll coverage from its label.
Can I use this for a hip roof?
Yes, if every roof plane has the same pitch: the sloped area of equal-pitch planes equals the plan area times the slope factor. For roofs with several pitches, measure each plane and use Roof area mode.
Can I use metric measurements?
Yes. Switch to meters and enter coverage per bundle in square meters. Results show square meters alongside roofing squares, which are always 100 square feet.
Related calculators and guides
Calculators
- Roof Pitch Calculator — Pitch as x/12, roof angle in degrees, slope percentage, and the sloped length for a given horizontal run.
- Drywall Calculator — Drywall sheet count for walls and ceilings from room dimensions or total area, minus openings, by sheet size.
- Paint Calculator — Gallons or liters of paint for your walls and number of coats, using the coverage printed on your paint's label.
Guides
- How to Measure an Irregular Area — Split odd shapes into rectangles, triangles, circles, and trapezoids, then average width and depth.
Sources
- How Many Square Feet in a Bundle of Shingles (IKO) — IKO Industries. Used for: 1 square = 100 sq ft; Cambridge 33.3 sq ft/bundle (3 per square); Armourshake 20 sq ft/bundle (5 per square). Checked 2026-10-04.
- TruDefinition Duration Shingles product page (Owens Corning) — Owens Corning. Used for: 3 bundles per square; 98.4 sq ft coverage per square (32.8 sq ft per bundle). Checked 2026-10-04.
- NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity — National Institute of Standards and Technology. Used for: 1 ft = 0.3048 m (exact); 1 in = 2.54 cm (exact). Checked 2026-10-03.