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Roofing Calculator

Area 1

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No result yet. Enter length and width.

Pitch and shingles

This counts shingles for buying. It does not check the structure, the roof deck, ventilation, ice barrier or code requirements. Ask a roofing contractor or your local building department.

Roof pitch (rise in 12 in of run)

One pitch for the whole roof. Planes with different pitches: work them out one pitch at a time.

Starts at 3: the count Owens Corning, TAMKO and GAF publish for their standard 3-tab and architectural shingles. Some products differ, such as GAF Woodland at 4 a square. The count on the wrapper or data sheet of your shingle is the one to use.

Starts at 10%. GAF recommends adding 10–15% for trim allowance and waste, and more for valleys, dormers and complex roofs. One source and an estimating recommendation, not a rule: change it to suit your roof.

Optional. Starter strip and drip edge both run along the eaves and rakes: the GAF Timberline HDZ and Owens Corning Duration instructions put starter at the rakes as well as the eaves. Hip and ridge caps run along the hips and ridges.

The length one bundle covers, from the wrapper or data sheet. It differs by product: Owens Corning gives about 105 ft for Starter Strip Plus; ridge caps run 20 ft (GAF TimberTex), 29.53 ft (IKO Hip & Ridge 12) or 33.3 ft (Owens Corning RIZERidge) a bundle.

Optional; uses the eaves and rakes length. Gibraltar and Englert sell drip edge in 10 ft pieces; others differ, so check yours. Pieces overlap where they join, so the count adds nothing for the laps: enter the piece length less your overlap to allow for it.

Optional; enter the roll length and width to count rolls. Each course overlaps the one below, which takes the overlap off the roll's width: Owens Corning gives 937 sq ft for a 250 ft × 48 in roll with a 3 in overlap; Malarkey asks for at least 4 in. Use your underlayment's instructions. End laps and the starter area are not counted.

Optional. Shingles per square is on the data sheet or wrapper (GAF Timberline HDZ: 64, in bundles of 20, 22 and 22). Only the shingles are counted, not the starter or ridge caps. Starts at 4: the standard pattern in the Owens Corning and GAF instructions. Both call for 6 a shingle on slopes steeper than 21/12 (60°), and some products, wind ratings and local codes call for 6 as well. The installation instructions of your shingle give the count to use.

Optional. From the box label, to count boxes.

Optional. Each price is multiplied by its own count; the total is the sum.

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How the shingle count is worked out

Start with the footprint. Measure each part of the roof as it looks from above, to the outside edge of the overhangs, and enter its length and width. A plain gable roof is two planes, one each side of the ridge; when every plane has the same pitch, the whole footprint can go in as one rectangle, because the planes together cover it exactly.

Pick the pitch: the inches the roof rises for every 12 in it runs across. An angle in degrees, or a rise and run you measured, works too; it becomes rise in 12 first. The slope factor is √(1 + (rise ÷ 12)²), which is how much longer the sloped roof is than the level run under it. Multiply the footprint by it to get the roof surface. Divide the surface by 100 sq ft, one roofing square, to get squares.

Add the waste allowance to the squares, multiply by the bundles that cover one square, and round up to a whole bundle. That is the number of shingle bundles to buy. Starter strip and ridge caps come in their own bundles: divide the length to cover by the length one bundle covers and round up. Drip edge pieces are the eaves and rakes ÷ the piece length. Underlayment rolls are the roof surface plus waste ÷ what one roll covers once the overlap between courses is taken off its width. Nails are the squares with waste × shingles per square × nails per shingle. Enter a price for any item and the cost adds them up.

The count is for buying shingles only. It does not look at the roof deck, the framing, ventilation, ice barrier or code requirements; a roofing contractor or your building department can tell you what your roof needs before you buy.

Examples

Gable roof, two planes: Area 1: 40 ft × 15 ft; Area 2: 40 ft × 15 ft

  1. Area 1 plan area: 40 ft × 15 ft = 600 sq ft = 55.74 m²
  2. Area 2 plan area: 40 ft × 15 ft = 600 sq ft = 55.74 m²
  3. Total area: 600 sq ft + 600 sq ft = 1,200 sq ft = 111.48 m²
  4. Slope factor, 6/12 pitch: √(1 + (6 ÷ 12)²) = 1.118
  5. Roof surface area: 1,200 sq ft × 1.118 = 1,341.6 sq ft = 124.64 m²
  6. Squares: 1,341.6 sq ft ÷ 100 sq ft = 13.42 squares
  7. With 10% waste: 13.42 squares + 10% = 14.76 squares
  8. Shingle bundles to buy: 14.76 squares × 3 bundles per square, rounded up = 45 bundles

45 bundles 14.76 squares with 10% waste. Plan area: 1,200 sq ft. Roof surface area: 1,341.6 sq ft. Squares: 13.42 squares.

Steeper roof with starter strip, ridge caps and a price: 52 ft × 30 ft

  1. Plan area: 52 ft × 30 ft = 1,560 sq ft = 144.93 m²
  2. Slope factor, 5/12 pitch: √(1 + (5 ÷ 12)²) = 1.083
  3. Roof surface area: 1,560 sq ft × 1.083 = 1,690 sq ft = 157.01 m²
  4. Squares: 1,690 sq ft ÷ 100 sq ft = 16.90 squares
  5. With 15% waste: 16.90 squares + 15% = 19.43 squares
  6. Shingle bundles to buy: 19.43 squares × 3 bundles per square, rounded up = 59 bundles
  7. Starter strip bundles: 170 ft ÷ 105 ft per bundle, rounded up = 2 bundles
  8. Hip and ridge bundles: 52 ft ÷ 33.3 ft per bundle, rounded up = 2 bundles
  9. Cost: 59 × $38.00 = $2,242.00

59 bundles 19.43 squares with 15% waste. Plan area: 1,560 sq ft. Roof surface area: 1,690 sq ft. Squares: 16.90 squares. Starter strip bundles: 2 bundles. Hip and ridge bundles: 2 bundles. Estimated cost: $2,242.00.

Every item priced, with drip edge, synthetic underlayment and nails: 40 ft × 30 ft

  1. Plan area: 40 ft × 30 ft = 1,200 sq ft = 111.48 m²
  2. Slope factor, 6/12 pitch: √(1 + (6 ÷ 12)²) = 1.118
  3. Roof surface area: 1,200 sq ft × 1.118 = 1,341.6 sq ft = 124.64 m²
  4. Squares: 1,341.6 sq ft ÷ 100 sq ft = 13.42 squares
  5. With 10% waste: 13.42 squares + 10% = 14.76 squares
  6. Shingle bundles to buy: 14.76 squares × 3 bundles per square, rounded up = 45 bundles
  7. Starter strip bundles: 140 ft ÷ 105 ft per bundle, rounded up = 2 bundles
  8. Drip edge pieces: 140 ft ÷ 10 ft per piece, rounded up = 14 pieces
  9. Coverage per roll, overlap taken off: 250 ft × (48 in − 3 in) = 937.5 sq ft = 87.10 m²
  10. Underlayment rolls: (1,341.6 sq ft + 10%) ÷ 937.5 sq ft, rounded up = 2 rolls
  11. Roofing nails: 14.76 squares × 64 shingles × 4 nails, rounded up = 3,779 nails
  12. Boxes of nails: 3,779 ÷ 7,200 per box, rounded up = 1 box
  13. Cost: 45 × $38.00 + 2 × $35.00 + 2 × $95.00 + 14 × $9.00 + 1 × $60.00 = $2,156.00

45 bundles 14.76 squares with 10% waste. Plan area: 1,200 sq ft. Roof surface area: 1,341.6 sq ft. Squares: 13.42 squares. Starter strip bundles: 2 bundles. Drip edge pieces: 14 pieces. Underlayment rolls: 2 rolls. Roofing nails: 3,779 nails, 1 box. Estimated cost: $2,156.00.

Pitch measured as 30 in of rise over 72 in of run: 52 ft × 30 ft

  1. Plan area: 52 ft × 30 ft = 1,560 sq ft = 144.93 m²
  2. Pitch as rise in 12: 12 × 30 ÷ 72 = 5/12
  3. Slope factor, 5/12 pitch: √(1 + (5 ÷ 12)²) = 1.083
  4. Roof surface area: 1,560 sq ft × 1.083 = 1,690 sq ft = 157.01 m²
  5. Squares: 1,690 sq ft ÷ 100 sq ft = 16.90 squares
  6. With 15% waste: 16.90 squares + 15% = 19.43 squares
  7. Shingle bundles to buy: 19.43 squares × 3 bundles per square, rounded up = 59 bundles

59 bundles 19.43 squares with 15% waste. Plan area: 1,560 sq ft. Roof surface area: 1,690 sq ft. Squares: 16.90 squares.

Shingle bundles by roof footprint and pitch: 10% waste, 3 bundles per square

Roof planeShingle bundles to buyPlan areaRoof surface areaSquares
40 ft × 25 ft, 4/1235 bundles1,000 sq ft1,054.1 sq ft10.54 squares
40 ft × 25 ft, 6/1237 bundles1,000 sq ft1,118 sq ft11.18 squares
50 ft × 30 ft, 4/1253 bundles1,500 sq ft1,581.1 sq ft15.81 squares
50 ft × 30 ft, 6/1256 bundles1,500 sq ft1,677.1 sq ft16.77 squares
50 ft × 40 ft, 6/1274 bundles2,000 sq ft2,236.1 sq ft22.36 squares
50 ft × 40 ft, 8/1280 bundles2,000 sq ft2,403.7 sq ft24.04 squares

One square is 100 sq ft of roof surface. Bundles per square used: 3. Check it against the wrapper or data sheet of your shingle, which is the count to trust.

Questions

Does this tell me whether my roof can take new shingles?

No. It counts shingles for buying. It does not check the structure, the roof deck, ventilation, ice barrier or what your local code requires, and it does not say whether a new layer can go over the old one. Ask a roofing contractor or your local building department about those.

What is a roofing square?

100 square feet of roof surface. Owens Corning and the NRCA roofing manual both define it that way, and shingles are priced and packed by the square.

Why do I measure the footprint and not the roof itself?

The footprint, measured on the ground or from a plan, is safer to get than a tape run up a roof. The pitch turns it into the sloped surface. Measure to the outside of the overhangs, because the shingles cover them too.

How does the pitch change the area?

A 6/12 roof rises 6 in for every 12 in it runs across. Each foot of run is then √(1 + (6 ÷ 12)²) = 1.118 ft of roof, by Pythagoras, so the surface is 1.118 times the footprint. The factors match the IKO estimating table, from 1.031 at 3/12 to 1.414 at 12/12.

Can I enter the pitch in degrees, or as a rise and run I measured?

Yes. An angle becomes rise in 12 as 12 × tan(angle), so 26.57° is 6/12. A rise and run you measured, in any one unit, becomes 12 × rise ÷ run, so 30 in over 72 in is 5/12. The working shows the conversion before the slope factor.

What is the lowest pitch for shingles?

GAF says its shingles must go on slopes of 2/12 or more. From 2/12 to under 4/12, GAF and Owens Corning both call for low-slope underlayment, two layers or a self-adhered membrane, in their installation instructions. The calculator still counts the material and shows a note; whether shingles suit your roof is a question for a roofer or your building department.

Is 3 bundles per square right for my shingles?

For most standard 3-tab and architectural shingles, yes. Owens Corning Supreme and Oakridge, TAMKO Elite Glass-Seal and Heritage and GAF Timberline HDZ all list 3 bundles per square. Some products differ; GAF Woodland, for example, comes 4 to a square. Read the wrapper or the data sheet and type its number in.

How much waste should I add?

The field starts at 10%. GAF recommends adding 10–15% for trim allowance and waste, and more for valleys, dormers and other complex roof shapes. That is one manufacturer's estimating advice, not a rule, so raise it for a cut-up roof.

How do I count starter strip and ridge caps?

Add the lengths of the eaves and rakes for starter strip, and of the hips and ridges for ridge caps, then type the length one bundle covers from its wrapper. The GAF Timberline HDZ and Owens Corning Duration instructions both put starter along the rakes as well as the eaves. Figures vary by product. Owens Corning gives about 105 ft a bundle for Starter Strip Plus; ridge caps run 20 ft a bundle for GAF TimberTex, 29.53 ft for IKO Hip & Ridge 12 and 33.3 ft for Owens Corning RIZERidge. The site has no default for either.

How is drip edge counted?

Drip edge runs along the eaves and rakes, the same length as the starter strip, and is sold in pieces. Pieces = that length ÷ the piece length, rounded up. Gibraltar and Englert sell 10 ft pieces, which the quick choice fills in; check yours. Pieces overlap where they join, and the count adds nothing for that, so enter the piece length less the overlap to allow for it.

My roof planes have different pitches. What do I do?

The calculator uses one pitch for the whole roof. Work out the planes of each pitch separately and add the bundles, or enter the steeper pitch for the whole roof to stay on the safe side.

How are underlayment rolls counted?

Each course overlaps the one below, so a roll covers its length × (its width − the overlap). Owens Corning gives 937 sq ft for a 250 ft × 48 in roll with a 3 in overlap, the same arithmetic. Rolls = roof surface plus waste ÷ that coverage, rounded up. The quick choices fill in synthetic rolls of 48 in × 250 ft (Owens Corning Deck Defense, Malarkey Secure Start SG) and

How many roofing nails do I need?

Nails = squares with waste × shingles per square × nails per shingle. Shingles per square is on the data sheet; GAF Timberline HDZ, for one, is 64. Nails per shingle starts at 4, the standard pattern in the Owens Corning and GAF instructions; both call for 6 on slopes over 21/12, and some products, wind ratings and local codes call for 6 too. Enter the count on the nail box to get boxes. Starter, ridge caps and flashing take nails of their own, which are not counted.

Does it count flashing, vents or ice barrier?

No. Step and valley flashing, vents and ice and water barrier depend on the roof's details. A roofer can take those off your roof.

Related tools

Sources

The square, 100 sq ft of roof, is defined by both Owens Corning and the NRCA manual. The starting count of 3 bundles per square is what Owens Corning, TAMKO and GAF publish for their standard shingles. The 10% starting waste rests on one GAF recommendation and is yours to change. The slope factor is plain geometry, checked against the IKO estimating table; the slope limits and the starting 4 nails per shingle are from the GAF and Owens Corning installation instructions. The underlayment roll sizes and the 10 ft drip edge piece offered as quick choices each rest on two makers' data. Starter strip and ridge cap coverage, shingles per square and the underlayment overlap are your entries. The unit definitions are from NIST.

Methodology and sources

Last reviewed: October 8, 2026