Roofing calculator
Roof square footage, roofing squares and shingle bundles from your house size and roof pitch, with cost per square or per bundle.
Your roof adds up to
13.95 squares
- Shingle bundles
- 42
- Roof area
- 1,268 sq ft
- Squares before waste
- 12.68
- Eaves and rakes (drip edge, starter)
- 144.4 ft
- Ridge and hips
- 42.0 ft, 2 cap bundles
- Estimated material cost
- A 6/12 roof is below the IRC minimum of 2/12 for this roofing. See the table below and check your local code.
- Below 4/12, the IRC calls for double underlayment under asphalt shingles.
One square covers 100 sq ft of roof. Squares include your 10% waste; the roof area is 1,134 sq ft of flat area × a 1.118 pitch multiplier. Bundles per square vary by shingle, so check the wrapper. Cap bundles assume a typical 35 ft per bundle. Edges assume the same overhang all around.
How to calculate roof square footage
A sloped roof has more surface than the floor under it. The calculator finds the flat area the roof covers, including overhangs, and multiplies it by the pitch multiplier from the roof pitch calculator. Roofers then count in squares of 100 sq ft, and shingles are sold in bundles, usually three to a square.
- Flat area = (length + 2 × overhang) × (width + 2 × overhang), in square feet
- Pitch multiplier = √(1 + (pitch ÷ 12)²)
- Roof area = flat area × multiplier. This holds for gable, hip and shed roofs as long as every slope has the same pitch.
- Squares = roof area ÷ 100, plus your waste percentage
- Bundles = squares × bundles per square, rounded up
- Edges: eaves are the level bottom edges, rakes the sloped gable edges (each the run × multiplier), and hips the sloped corners of a hip roof
Worked example
A 40 × 25 ft house with a 12 inch overhang and a 6/12 gable roof: the roof covers 42 × 27 = 1,134 sq ft of flat area. The 6/12 multiplier is 1.118, so the roof area is 1,134 × 1.118 = 1,268 sq ft, or 12.68 squares. With 10% waste that's 13.95 squares, and at 3 bundles per square, 13.95 × 3 rounds up to 42 bundles. The eaves and rakes add up to 144.4 ft of drip edge, and the 42 ft ridge takes 2 bundles of cap shingles.
Roof area by pitch
For every 1,000 sq ft of flat area under the roof (the house plus its overhangs), with 10% waste and 3 bundles per square.
| Pitch | Multiplier | Roof area, sq ft | Squares with waste | Bundles |
|---|---|---|---|---|
| 0/12 | 1.000 | 1,000 | 11.00 | 33 |
| 2/12 | 1.014 | 1,014 | 11.15 | 34 |
| 3/12 | 1.031 | 1,031 | 11.34 | 35 |
| 4/12 | 1.054 | 1,054 | 11.60 | 35 |
| 5/12 | 1.083 | 1,083 | 11.92 | 36 |
| 6/12 | 1.118 | 1,118 | 12.30 | 37 |
| 7/12 | 1.158 | 1,158 | 12.73 | 39 |
| 8/12 | 1.202 | 1,202 | 13.22 | 40 |
| 9/12 | 1.250 | 1,250 | 13.75 | 42 |
| 10/12 | 1.302 | 1,302 | 14.32 | 43 |
| 12/12 | 1.414 | 1,414 | 15.56 | 47 |
Minimum roof pitch by material
From the International Residential Code (IRC) R905.2.2 and R905.10.2. Local codes and the manufacturer's instructions can require more, so check with your building department.
| Roofing | Minimum pitch | Notes |
|---|---|---|
| Asphalt shingles | 2/12 | Double underlayment from 2:12 up to 4:12. IRC R905.2.2 |
| Metal panels, lapped seams without sealant | 3/12 | IRC R905.10.2 |
| Metal panels, lapped seams with applied lap sealant | 0.5/12 | Sealant per the manufacturer's instructions. IRC R905.10.2 |
| Metal panels, standing seam | 0.25/12 | IRC R905.10.2 |
Roofing questions
How many bundles of shingles make a square?
Usually three. A square of shingles covers 100 sq ft of roof, and according to Mike Guertin in Fine Homebuilding, three bundles to a square is most common: most three-tab shingles and some lightweight laminated (architectural) shingles. Heavier three-tab and laminated shingles take four, or sometimes five, bundles per square. The wrapper says which, so choose it above. A 1,268 sq ft roof is 12.68 squares, or 13.95 squares with 10% waste.
How do I measure a roof for shingles?
The most accurate way is to measure each roof plane on the roof and add them up, then choose "Roof area" above. From the ground, measure the house's length and width, estimate the overhang, and find the pitch (the roof pitch calculator shows how to measure it from the attic or a gable end); "House size" does the rest. If you know the flat area from a plan or a satellite measurement, choose "Flat area" and the calculator applies the pitch multiplier. Stay off steep or wet roofs.
How much waste should I add for shingles?
It depends on how cut-up the roof is. Guertin figures about 1% waste for a simple roof and 5% or more for a complex roof with open valleys, and says fall-off at gable ends, valley trimmings and damaged shingles can add up to another 5%. Every hip, valley, dormer and chimney means more cut shingles. This calculator starts at 10% as a cushion. Lower it for a plain gable if you're confident in your measurements, and raise it for a hip roof or lots of valleys.
How much starter, drip edge and ridge cap do I need?
Starter shingles go along the eaves and rakes, and so does drip edge, so the calculator adds those edges up for you. Guertin counts starters from the eave and rake length divided by the 3 ft length of a strip shingle; dedicated starter products list their own coverage. Cap shingles cover the ridge and hips and usually cap about 35 linear feet per bundle, but products vary, so check the bundle. A 50 × 30 ft hip roof with an 18 inch overhang at 6/12 has 172 ft of eaves, a 20 ft ridge and 99.0 ft of hips, about 4 bundles of cap.
How do I calculate a metal roof?
The roof area and squares are the same as for shingles; choose "Metal panels" above. How many panels you need depends on the panel's coverage width and the length of each slope, so use the manufacturer's coverage figure when you order. The IRC allows metal panels at lower pitches than shingles: 0.25/12 for standing seam, 3/12 for lapped seams without sealant, against 2/12 for asphalt shingles.
How do I estimate the cost of a roof?
Enter a price per square or per bundle above. Shingles are often priced per bundle at the store, while roofers usually quote per square installed. Prices vary a lot by region, material and roof, and an installed price also covers labor, tear-off, underlayment, flashing and disposal, so get quotes for a replacement and use this to check the quantities on them.