Shingle Calculator
Find out how many bundles of asphalt shingles to buy for your roof, measured from the ground.
Roof dimensions
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For a 40 ft × 30 ft footprint with a 6/12 pitch and 10% waste, at 3 bundles per square, you'll need about 45 bundles of shingles.
Shingle bundles needed
45 bundles
That's a typical full-house reroof — in the range where most single-family homes land.
At this volume — well over a ton of material — arrange rooftop boom-truck delivery from your supplier rather than hand-carrying, and explicitly request all bundles from one production lot so color stays consistent across every plane.
True roof surface area (before waste): 1342 sq ft
Roofing squares (with waste): 14.8 squares
Raw computed amount: 44.27 bundles
How this works
The calculation runs in four steps, each of which you can check by hand. First, the horizontal footprint area is your length times width — this is the roof's projection onto flat ground, the thing you can measure with a tape without leaving the ground (remember to include eave and rake overhangs, not just wall-to-wall distance). Second, that footprint is multiplied by the pitch multiplier for the slope you select — geometrically, the multiplier is sqrt(rise² + run²) ÷ run, the ratio between a sloped surface and its shadow, so a 6/12 roof carries 1.118× its footprint in actual shingled surface and a 12/12 roof carries 1.414×. Third, a waste allowance is added — 10% for a simple gable roof, 15% for roofs with hips, valleys, or dormers — covering starter courses, ridge and hip caps cut from field shingles, valley cuts, and edge trimming. Fourth, the resulting area is converted to roofing squares (one square = exactly 100 sq ft) and multiplied by bundles per square — 3 for standard shingles, adjustable for heavyweight products — then rounded up to the next whole bundle, because that's the unit shingles are sold in. The bundles-per-square packaging convention and the waste guidance come from published manufacturer estimating guidance Owens Corning, "How Many Shingles Do I Need?" (3 bundles per square; ~10–15% waste).
Worked example
A 40 ft × 30 ft house footprint with a 6/12 roof, using the default 3 bundles per square and 10% waste: the footprint is 1,200 sq ft, and the 6/12 pitch multiplier of 1.118 brings the true roof surface to about 1,342 sq ft. Adding 10% waste gives 1,476 sq ft — about 14.8 squares. At 3 bundles per square, that's 44.3 raw bundles, rounded up to 45 bundles, since shingles are sold by the whole bundle.
A second example: a steeper, more complex roof
The same 40 ft × 30 ft footprint, but with a steep 10/12 roof featuring hips and a valley, so the 15% complex-roof waste setting applies: the 10/12 multiplier of 1.302 turns 1,200 sq ft of footprint into about 1,562 sq ft of roof surface. With 15% waste that's 1,796 sq ft — 18.0 squares — and at 3 bundles per square, 53.9 raw bundles, rounded up to 54. Note the jump from 45 to 54 bundles for the same footprint: pitch and complexity together added 20% to the order. That's why guessing the pitch instead of measuring it is the most expensive shortcut in a shingle estimate.
Common mistakes
Measuring wall-to-wall and forgetting the overhangs
The roof extends past the walls at the eaves and rakes, typically 6 to 24 inches per side. Measuring the building's wall footprint instead of the roof's projection undercounts area on every side at once — on a 40×30 ft house with 1 ft overhangs all around, that's an entire square (about 3 bundles) of missing roof.
Using the footprint area without a pitch multiplier
A 6/12 roof has almost 12% more surface than its footprint; a 12/12 roof has 41% more. Ordering off raw footprint area is the single biggest systematic underestimate in DIY roofing orders, and it grows with pitch — exactly on the steep roofs where a second supply run is most disruptive.
Skipping waste because the roof 'looks simple'
Even a plain gable roof consumes extra shingles for starter courses along both eaves, ridge caps along the full ridge, and edge trimming. The 10% simple-roof allowance is the floor, not padding. Valleys, hips, and dormers push real-world waste toward 15%, which is why the calculator offers that as a selectable option.
Assuming every shingle product is three bundles per square
Heavyweight architectural and designer shingles often package at four or five bundles per square because a three-bundle split would be too heavy to handle. If you price a job assuming three and your chosen product is four, your material budget is instantly 33% off. The bundle wrapper always states coverage — check it before ordering.
Ordering across different production lots
Shingle color varies subtly between manufacturing lots, and the difference that's invisible in a warehouse is visible as banding across a roof plane in afternoon sun. Order the full quantity at once and ask the supplier to pull from a single lot — one more reason to get the estimate right the first time rather than topping up later.
Forgetting dormers, porches, and attached garage roofs
The main roof footprint is easy to remember; the porch roof, bay-window roof, and dormer faces are easy to forget. Each is small on its own, but together they commonly add a square or two. Walk the whole building and list every surface that will receive shingles before settling on your footprint dimensions.
Treating the bundle estimate as the whole material list
Field shingles are the biggest line item but not the only one: underlayment, ice-and-water barrier at eaves and valleys (required by code in cold climates), drip edge, ridge caps, starter strips, and roofing nails (roughly 320 nails per square at 4 nails per shingle) all scale with the same squares figure this calculator reports — use it to size those purchases too.
When this calculator's model stops applying
- Roofs with multiple pitches (a steep main roof over a low-slope porch, a gambrel barn profile): the single-multiplier model breaks. Calculate each pitch section separately with its own footprint and multiplier, then sum the bundles.
- Very complex roofs — multiple intersecting hips, turrets, many dormers: waste can exceed even 15%, and the footprint-projection method starts missing vertical dormer cheeks and other surfaces. For these, a plane-by-plane takeoff (measuring each roof plane individually) is the reliable method, and this calculator becomes a sanity check rather than an order quantity.
- Low-slope and flat roofs below about 2/12: asphalt shingles are generally not warranted below 2/12 pitch at all, and require special underlayment procedures between 2/12 and 4/12. Below that threshold you're shopping for rolled roofing or membrane, which is estimated by area, not bundles.
- Re-roofing over an existing layer versus tearing off: the shingle quantity is the same, but the decision affects everything else — weight limits, code limits on layer count (most US codes allow a maximum of two layers), and whether your waste percentage should account for matching into existing flashing details.
- Metric-market shingle products: this calculator's bundle logic reflects US packaging (bundles per 100 sq ft square). Metric-dimensioned shingles sold outside North America state coverage per bundle in m² — enter dimensions in metric by all means, but confirm coverage from the local product's wrapper.
- Mansard and other near-vertical surfaces: at pitches much beyond 12/12 the multiplier grows quickly (an 18/12 mansard face has a multiplier of 1.80) and small pitch-estimation errors swing the answer hard. Measure the actual rise and run rather than eyeballing, or measure the sloped face directly if it's accessible.
- Roofs with large penetrations — big skylights, wide chimneys, solar arrays being installed simultaneously: the calculator doesn't subtract penetration area. For a normal chimney or a couple of vent stacks that's correctly ignored (the offcuts around them are waste anyway), but a bank of skylights covering several squares is worth subtracting from your footprint area manually.
FAQ
What exactly is a roofing 'square'?
A square is the roofing industry's standard area unit: exactly 100 square feet of roof surface. Shingles, underlayment, and roofing labor are all quoted per square, which is why this calculator reports your roof size in squares alongside the bundle count — it's the number a roofer or supplier will actually talk in.
Why three bundles per square?
Standard three-tab and most common architectural asphalt shingles are packaged so that three bundles cover one square (100 sq ft) when installed at the manufacturer's specified exposure. That's a packaging convention, not a law of nature: some heavyweight designer and luxury architectural shingles ship at four or even five bundles per square because each shingle is thicker and the bundle would otherwise be too heavy to carry up a ladder. Check the wrapper of your specific product and adjust the bundles-per-square field if it differs.
Why do I enter the building footprint instead of the actual roof size?
Because the footprint is what you can measure safely from the ground. The roof surface is larger than the footprint by a factor that depends only on the slope — the pitch multiplier. This calculator multiplies your footprint area by the multiplier for the pitch you select, which reproduces the true sloped area without anyone climbing on the roof with a tape measure.
How do I figure out my roof's pitch?
From inside the attic, hold a level horizontally against a rafter, measure 12 inches along the level from the point of contact, then measure vertically from the 12-inch mark down to the rafter — that vertical distance in inches is your pitch in X/12 notation. Our Roof Pitch Calculator does the conversion from any rise and run measurement to pitch, angle, and multiplier.
Is 10% waste really necessary?
Yes, and sometimes more. Every ridge and hip needs cap shingles, every valley requires shingles cut at an angle (the offcuts are usually unusable), the first course of every roof plane needs a starter strip, and edges need trimming to line. Owens Corning's guidance is roughly 10% for a simple gable roof and up to 15% for complex roofs with hips, valleys, and dormers. Running out mid-roof is worse than the cost of a couple of extra bundles — an exposed deck and a closed supplier is a bad combination.
Does this calculator include underlayment, ridge caps, or starter strips?
No — it estimates field shingle bundles only. Underlayment (felt or synthetic) is bought by roof area in squares, so the squares figure this tool reports is directly reusable for that purchase. Ridge caps and dedicated starter strips are bought by linear footage of ridge/hip and eave respectively; the waste allowance covers cutting field shingles for those roles on smaller jobs, but a dedicated product is the better practice on a full reroof.
What about overhangs (eaves) that extend past the walls?
The footprint you enter should be the roof's horizontal projection, not the wall-to-wall building dimension. If your eaves overhang the walls by a foot on each side, add two feet to each footprint dimension. Forgetting overhangs is one of the most common causes of underestimating by half a square or more on a typical house.
Can I use this for a hip roof, or only a gable roof?
The footprint-times-multiplier math gives the same total surface area for a hip roof as for a gable roof of the same footprint and pitch — the geometry works out identically as long as all planes share the same pitch. What changes is waste: hips add four or more angled cut lines, so select the higher 15% waste setting rather than the 10% simple-roof default.
How heavy are shingle bundles, and does that matter for delivery?
A typical architectural shingle bundle weighs 60–80 pounds, so a modest 45-bundle job is roughly a ton and a half of material. Most suppliers offer rooftop delivery, placing bundles directly on the roof by boom truck — worth arranging, because carrying that weight up a ladder bundle by bundle is a genuinely punishing job and stacking a full pallet in one spot on a driveway can be a problem too.
Should I round my answer up or down?
Always up — this calculator already rounds the raw bundle figure up to the next whole bundle, because shingles are sold by the bundle, not by the shingle. Leftover full bundles are usually returnable unopened, and keeping one opened bundle for future repairs in a matching color and lot is standard practice, since shingle colors weather and get discontinued.
My roof has two different pitches. What do I do?
Split it: run the calculator once for each section, entering the footprint area under each pitch, then add the bundle totals. Summing separately is more accurate than averaging the pitch, because the multiplier isn't linear in pitch — a steep section contributes more extra area than the average suggests.
Can I switch between imperial and metric partway through?
Yes — the unit toggle converts every field you've already entered, so you won't lose your measurements. Internally the tool always computes from the same canonical values regardless of which unit is displayed, so switching back and forth doesn't introduce rounding error. The bundle count itself is unit-independent — a bundle is a bundle in any system.
Related tools
Roof Pitch Calculatorif you don't know your roof's pitch yet, measure a rise and run and get the exact pitch multiplier this calculator's presets are built from.More roofing tools (underlayment and roofing-nail estimators) are planned but not yet published.