Roof Shingle Calculator
This roof shingle calculator turns your house footprint and roof pitch into squares, shingle bundles, underlayment rolls, and nails. Enter the footprint length and width in feet or meters, pick a pitch from 1/12 to 12/12, set your waste percentage, and it applies the roofer’s slope multiplier for you.
Shingle bundles to buy
45bundles
- Roof surface area (6/12 pitch)1,342 sq ft
- With 10% waste — order1,476 sq ft (14.8 squares)
- Underlayment2 synthetic rolls or 8 rolls of #30 felt
- Roofing nails (~320 per square)≈ 4,750 nails
Formulas last reviewed on .
How footprint and pitch become bundles
A sloped roof is bigger than the house under it, and the pitch multiplier says exactly how much bigger:
roof area = footprint × multiplier
squares = roof area × (1 + waste) ÷ 100
bundles = ceil(squares × 3)
Pitch is the rise per 12 units of run, so a 6/12 roof climbs 6 inches for every 12 it travels. The multiplier is straight Pythagoras — the sloped surface is the hypotenuse over your flat footprint — and it grows fast: a 12/12 roof carries 41% more shingles than the footprint suggests. Measure the footprint at the eaves so the overhangs are included; a flat-area roofing calculator that skips this slope step will short you by whole squares.
A square is 100 square feet, and standard three-tab or architectural shingles run three bundles per square. The 10% default waste suits a simple gable roof — bump it to 15% for hips and valleys, where every course gets an angled cut. Underlayment is figured both ways: one synthetic roll covers about 10 squares (a standard 48-inch × 250-foot roll is 1,000 sq ft), one roll of #30 felt about 2. Nails run roughly 320 per square at the standard 4 per shingle.
Worked example: a 40 × 30 gable-roof ranch
Take a rectangular ranch, 40 feet by 30 feet at the eaves, wearing a plain 6/12 gable roof — the calculator’s default inputs, so the result box above shows this exact math.
- Footprint: 40 × 30 = 1,200 sq ft.
- Multiplier: √(1 + (6 ÷ 12)²) = √1.25 = 1.118.
- Roof area: 1,200 × 1.118 = 1,342 sq ft of actual sloped surface — the pitch added 142 square feet you’d never see from the driveway.
- Waste: ×1.10 = 1,476 sq ft, or 14.8 squares.
- Bundles: 14.758 squares × 3 = 44.3, rounded up to 45 bundles.
- Underlayment and nails: 2 synthetic rolls (or 8 rolls of #30 felt) and roughly 4,750 roofing nails — call it two 30-pound boxes of coil nails.
Forty-five bundles is about 3,400 pounds of shingles. If the delivery truck can’t boom them onto the roof, plan your staging — carrying 75-pound bundles up a ladder is the part of roofing nobody prices in.
What is the roof pitch multiplier for a 1/12 to 12/12 pitch?
Every pitch from 1/12 to 12/12, its angle in degrees, the exact multiplier, and what that does to 1,000 square feet of footprint. This is the whole reason two houses with identical footprints can differ by four squares of shingles.
| Pitch | Roof angle | Multiplier | Roof area per 1,000 sq ft footprint |
|---|---|---|---|
| 1/12 | 4.8° | 1.003 | 1,003 sq ft |
| 2/12 | 9.5° | 1.014 | 1,014 sq ft |
| 3/12 | 14.0° | 1.031 | 1,031 sq ft |
| 4/12 | 18.4° | 1.054 | 1,054 sq ft |
| 5/12 | 22.6° | 1.083 | 1,083 sq ft |
| 6/12 | 26.6° | 1.118 | 1,118 sq ft |
| 7/12 | 30.3° | 1.158 | 1,158 sq ft |
| 8/12 | 33.7° | 1.202 | 1,202 sq ft |
| 9/12 | 36.9° | 1.25 | 1,250 sq ft |
| 10/12 | 39.8° | 1.302 | 1,302 sq ft |
| 11/12 | 42.5° | 1.357 | 1,357 sq ft |
| 12/12 | 45.0° | 1.414 | 1,414 sq ft |
Two of these are worth memorizing: 9/12 is exactly 1.25 (it’s a 3-4-5 triangle), and 12/12 is √2. Below 4/12, most shingle manufacturers require special low-slope installation, and below 2/12 asphalt shingles are off the table entirely — check the wrapper before you buy for a shallow roof.
Frequently asked questions
How many bundles of shingles make a square?
Three bundles per square for standard three-tab and most architectural shingles — that’s the ×3 in this calculator. Heavier designer and triple-laminate shingles can run four or even five bundles per square, so check the coverage printed on the wrapper: it states exactly how many bundles cover 100 square feet. If yours says four, multiply the squares result above by 4 instead.
Can I estimate my roof without climbing on it?
Yes — that’s exactly what this calculator is built for. Measure the house footprint at ground level, add the eave and rake overhangs (commonly 1 to 2 feet per side), and estimate the pitch from a photo of the gable end or by counting rise over run on a ladder at the eave. The pitch multiplier then does the climbing for you. It won’t capture dormers or intersecting wings, so add their footprints separately.
How much waste should I add for a hip roof?
Use 15% instead of the 10% default. Hips and valleys force an angled cut at the end of nearly every course, and unlike a gable’s straight rake cuts, the offcuts are rarely reusable on the opposite side. Add the ridge caps on top of that — hip roofs have much more ridge and hip line to cap than a simple gable, and caps are cut from full shingles or bought as dedicated bundles.
Can I shingle over my old roof instead of tearing off?
Most codes allow a maximum of two layers of asphalt shingles, so one existing layer in decent shape can be roofed over — you’ll need longer nails and the new roof will telegraph any lumps beneath it. Tearing off is the better job: it exposes rotten decking, lets you install fresh underlayment and ice-and-water shield, and removes several thousand pounds of dead load. Two existing layers means tear-off, no debate.
Do I need extra shingles for starter strips and ridge caps?
Yes, a little. Starter strip runs the eaves (and ideally the rakes) — dedicated starter rolls cover about 100 linear feet per bundle, or you can cut tabs off field shingles. Ridge caps cover roughly 25 to 35 linear feet per bundle depending on brand. For the 40 × 30 example, that’s 80 feet of eaves and 30-odd feet of ridge: one starter bundle and one or two cap bundles on top of the 45 field bundles.
These results are planning estimates only — verify quantities with your supplier and local building code before you buy or build. See our terms of use.