Roofing squares and bundles
Enter the building footprint, the overhang and the pitch, and get the shingle order: how many squares of roof, how many bundles, and the starter strip, ridge cap and underlayment that go with them.
Eave to eave
Along the ridge
Past the wall, every side
Rise per foot of run
Cuts, starter and ridge trim, and a few extra
17.0 squares of roof
51bundles
Roof area
1543 sq ft
Underlayment
2 rolls
Nails
16,320
Why the roof is bigger than the building
The footprint is 1232 square feet, but the roof over it is 1543 — the plan area (including the overhang) times 1.1180, the same slope factor a common rafter's own length bears to its run at 6:12. A flatter roof barely grows past its footprint; a steep one adds nearly half again.
Order this
- Shingle bundles16.97 squares, 10% waste included
- 51
- Starter stripBoth eaves — check whether your shingle brand sells a dedicated starter or wants inverted shingles
- 92 ft
- Ridge capOne ridge run, including the rake overhang at each end
- 46 ft
- UnderlaymentSynthetic felt at roughly 1,000 sq ft a roll — doubled below the pitch this page checks for
- 2 rolls
- Roofing nailsFour per shingle, the standard pattern
- 16,320
Where to buy this
- 51 shingle bundlesHome DepotLowe's
- 92 ft starter stripHome DepotLowe's
- 46 ft ridge capHome DepotLowe's
Shingle colour and line have to match across bundles, so buy the whole roof in one go from one lot.
Plain search links, nothing sponsored. Prices and stock are the shop's, and a local lumberyard will usually beat both on solid stock.
Against the model code
- At least 2:12 for asphalt shingles — passesThis roof is 6:12, which is steep enough for asphalt shingles.
- Doubled underlayment under 4:12 — passesThis roof is 6:12, steep enough for a single layer of underlayment.
The slope limits are the 2021 IRC's (R905.2.2). They are defaults, not law where you are building — jurisdictions amend them, and a shingle maker's own warranty often asks for more than the code does. Ring your building department, and read the wrapper.
This is a simple gable
The waste percentage is doing double duty on a real roof: a plain gable needs little more than trim waste, but hips, valleys, dormers and a cut-up plan all eat far more material than their area suggests, because every one of those lines is a row of cut shingles instead of a full one. Push the waste figure to 15–20% for a hip roof and higher still for anything with valleys, or price the job by counting each roof plane separately.
About roofing shingles
- Why is a roof bigger than the building underneath it?
- Because it slopes. A flat ceiling over a 30x40 building covers 1,200 square feet, but the roof above it at 6/12 covers about 1,342 — the footprint times 1.1180, the same slope factor a common rafter's own length bears to its run. A steeper roof grows faster: 12/12 multiplies the footprint by root two, 41% more roof than floor.
- How many bundles are in a square of shingles?
- Three, for both three-tab and the architectural shingles most roofs get today — one square is 100 square feet of coverage, and it is packaged three bundles to the square regardless of maker. That figure is printed on the wrapper of nearly every shingle bundle sold in North America.
- How much extra should I order for waste?
- Ten percent covers a plain gable roof — trim at the rakes, the starter course, the ridge cap. A hip roof wants 15–20%, because every hip is a line of angled cuts instead of full shingles, and a roof with valleys or dormers wants more again. Waste on a cut-up roof is not really waste; it is material that has nowhere flat to land.
- When does a roof need a doubled layer of underlayment?
- Below 4:12 (IRC R905.2.2). Asphalt shingles themselves are not rated under 2:12 at all — anything flatter than that wants a membrane roof or standing-seam metal instead, because water does not shed fast enough off a shallow slope to stay ahead of wind-driven rain finding its way under a shingle lap.
- Do starter shingles matter, or can I just flip a row upside down?
- A dedicated starter strip is worth buying. Inverted shingles work but their tabs are cut for a different overlap and their adhesive strip sits in the wrong place relative to the first course, which is exactly the row wind gets under first. Either way the starter needs to overhang the drip edge by about 1/4" to 3/8" at the eave and rake.