Roofing shingle calculator

Bundles and squares from the footprint you can measure on the ground.

Units

A 6/12 pitch rises 6 in over 12 in of run.

Why 10%?

Ten percent covers a simple gable. Hips, valleys and dormers all add cut waste, and a complex roof runs closer to fifteen percent — every valley turns full shingles into offcuts.

Add the rest of the roof

Total gutter edge. Sets the starter strip.

The sloping gable edges. Drip edge runs both.

Sets the hip and ridge cap.

Nailing
Add a price

Optional. Leave blank and the estimate shows quantities only.

Enter your roof footprint and pitch to see how many bundles it takes.

    Why a roof is bigger than the house under it

    You measure a roof on the ground and you cover it on the slope, and those are two different areas. The gap between them is the single largest source of short orders in roofing, and it is the first thing any roofing calculator has to get right before the bundle count means anything.

    multiplier = sqrt(1 + (rise / 12)²) roof area = footprint × multiplier squares = roof area / 100 bundles = ceil(squares × (1 + waste) × 3)

    Pitch multipliers

    3/12 → 1.031 6/12 → 1.118 9/12 → 1.250 4/12 → 1.054 7/12 → 1.158 10/12 → 1.302 5/12 → 1.083 8/12 → 1.202 12/12 → 1.414

    Worked example: 1,500 ft² at 6/12

    footprint = 1,500 ft² multiplier = 1.118 roof area = 1,677 ft² = 16.77 squares with 10% = 18.45 squares bundles = 56

    Order for the footprint instead and you buy 50 bundles for a roof that needs 56 — six bundles short, discovered on the last plane, in a colour batch that may no longer match.

    Common mistakes

    • Ordering the footprint. A 6/12 roof is twelve percent bigger than the ground it covers.
    • Ten percent waste on a hip roof. Cut waste on hips and valleys runs closer to fifteen.
    • Forgetting the accessories. Starter, ridge cap, underlayment and drip edge are separate.
    • Ordering exactly. Colour batches vary; a spare bundle now beats a mismatched one later.

    When this does not apply

    • Anything but standard architectural shingles. Three-tab, metal, tile and slate all cover differently.
    • Roofs with several different pitches. Work out each plane separately and add them.
    • Structural questions. Whether your deck can carry a second layer is not an arithmetic question.

    Under the shingles

    Shingles need a sound deck under them, and a re-roof often means replacing sheathing — the plywood calculator counts sheets across every size your yard stocks. If your roof is not a simple rectangle in plan, take the footprint from the square footage calculator and bring it back here.

    Pitch multiplier and bundles for a 1,500 ft² footprint

    PitchMultiplierRoof area (ft²)SquaresBundles at 10%
    3/121.031154615.552
    4/121.054158115.853
    5/121.083162516.354
    6/121.118167716.856
    7/121.158173717.458
    8/121.202180318.060
    9/121.250187518.862
    10/121.302195319.565
    12/121.414212121.271

    The multiplier is the whole point: the same building takes 50 bundles at 3/12 and 71 at 12/12. Measure the footprint on the ground, then apply your pitch.

    The rest of the roof

    Field shingles are the biggest line on the order and nowhere near all of it. Underlayment and nails follow the roof area, so the calculator counts them whatever you enter. Starter, ridge cap and drip edge follow lengths it cannot know — open Add the rest of the roof and give it your eaves, rakes and ridges, and they appear on the list.

    A worked roof: 1,500 ft² footprint at 6/12, 100 ft of eaves, 60 ft of rakes, 45 ft of ridge

    ItemBuy
    Bundle56
    Starter strip bundle1
    Hip and ridge bundle2
    Underlayment roll2
    10 ft drip edge16
    5 lb box of nails4
    1 lb box of nails3

    Underlayment is figured net of its published 4 in lap, so a roll covers 917 ft² rather than the 1,000 printed on it. Valley metal, ice and water shield and pipe boots are not counted — what each roof needs depends on your climate zone and local code.

    What goes on under it

    Below the shingles is a deck. The plywood calculator counts sheathing sheets, the square footage calculator takes a roof that is not one plain rectangle and gives you a footprint to bring back here, and the board foot calculator prices rafters and framing the way a yard quotes them. Re-roofing over a deck you are also building? The deck board calculator covers the boards, and the deck stain calculator finishes them.

    Section through a roof at a 6 in 12 pitch, showing why the sloped area exceeds the footprint.
    Drawn to scale.

    Common questions

    How many bundles of shingles do I need for a 1500 square foot roof?

    It depends entirely on the pitch, which is why "a 1500 square foot roof" is an ambiguous phrase. If 1500 is the ground footprint at a 6/12 pitch, the actual roof surface is 1,677 square feet — 16.8 squares — and with ten percent waste that is 56 bundles. If 1500 is the sloped area itself, it is 15 squares and about 50 bundles.

    What is a roofing square?

    One hundred square feet of roof surface. It is the unit the trade quotes and orders in, and it exists because it makes the arithmetic tidy: three bundles of standard architectural shingles cover one square, so squares times three gives bundles directly.

    How does roof pitch change the amount?

    A pitched roof has more surface than the ground it covers, and the multiplier grows fast. A 4/12 pitch adds five percent, a 6/12 adds twelve, a 9/12 adds twenty-five, and a 12/12 adds forty-one. Measuring your house from the ground and ordering that many squares is the most common way to come up short.

    How do I find my roof pitch without getting on the roof?

    From inside the loft, hold a level out horizontally against a rafter, mark 12 inches along it, and measure straight down from that mark to the rafter. That vertical measurement is your rise per 12 inches of run — a 6 inch drop is a 6/12 pitch. It is safer than the roof and accurate enough to order from.

    How much waste should I allow for roofing?

    Ten percent for a simple gable, and around fifteen for a hip roof or anything with valleys and dormers. The difference is cut waste: every valley turns full shingles into offcuts, and a hip roof has cut edges on the diagonals of every plane. If your roof has more than a couple of penetrations, budget toward the higher figure.

    What else do I need besides the shingles?

    Underlayment across the whole deck, starter strip along every eave, ridge cap along the ridges and hips, drip edge on eaves and rakes, and the nails. This calculator counts all of them. Underlayment and nails follow the roof area, so they are always there. The rest follow lengths only you can measure, so open "Add the rest of the roof" and give it your eaves, rakes and ridges — they are left out rather than guessed, because a rectangle and an L of the same area need very different lengths of each.

    How many nails per bundle of shingles?

    It is per shingle, not per bundle. IKO specify four nails for a standard application and six for steep slopes, and a bundle holds twenty shingles — so eighty to a hundred and twenty a bundle. At 1-1/4 inches a roofing nail runs 218 to the pound, so a 1,500 square foot roof at a 6/12 pitch takes about four and a half thousand nails, or twenty-odd pounds. Check your own wind zone: six-nail patterns are required in more places than people expect.

    How much underlayment do I need?

    Less per roll than the wrapper says. A synthetic roll is 250 feet by 48 inches and prints 1,000 square feet, but it laps four inches, so only 44 inches of each course is exposed — about 917 square feet of actual coverage. Ordering to the printed figure leaves you short by a roll on a large roof. This calculator uses the net figure.

    Sources

    Bundles per square is for architectural shingles. Stored for a later phase; no roofing calculation is implemented yet. Three bundles to a square is the common packaging but not universal: the IKO sheet cited here draws attention to it precisely because many laminated brands package to 97-99 percent of a square instead. Check the coverage printed on the bundle before ordering to the last unit. Nail box quantities are Grip-Rite's published SKU counts; the weights on the labels follow their own naming, and the 1, 30 and 50 lb sizes divide exactly by the 218-per-pound figure. Underlayment coverage is figured net of the published 4 in lap rather than from the 1,000 ft2 gross roll area, because a lapped roll does not cover its own area.

    Unit conversions are exact by definition and need no source.

    How we choose and cite these figures

    By Team MaterialMath. Published . Last checked . How these figures are sourced and checked.