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Shingle calculator
Put your roof size, bundles per square and waste in: a 40 ft by 25 ft roof is 1000 sq ft, or 10 squares — 30 bundles exact, 33 bundles with 10% waste.
★ CONSTRUCTION · ROOF · SHINGLES
Shingle Calculator: 33 Bundles for a 40×25 ft Roof
On the defaults — a 40 ft by 25 ft roof, 3 bundles per square, 10% waste — you need 33 bundles of shingles. This is the shingle tool: measure the slope once, allow for the cutting, and order the bundles once — a half-shingled roof waits for no second delivery.
What does shingle needed 33 bundles mean?
It means thirty-three bundles of shingles cover a 40 ft by 25 ft roof once cutting waste is allowed for. The roof itself is 40 times 25, or 1000 square feet; roofers divide by 100 and call that 10 squares, which is the unit shingles are sold by. At 3 bundles per square the bare count is 30 bundles, and the 10% waste allowance adds 3 bundles for the shingles cut at the hips, valleys and edges, taking the order to 33. The waste bundles are not spare stock exactly — they are the shingles the roof consumes in cutting, so a roof ordered without them comes up short at the last valley.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Roof area | length × width | 1000 sq ft — 40 × 25. |
| Squares | roof area ÷ 100 | 10 squares — 1000 ÷ 100. |
| Exact bundles | squares × bundles per square | 30 bundles — 10 × 3. |
| Bundles with waste | exact × (1 + waste ÷ 100), rounded up | 33 bundles — 30 × 1.10. |
Three things to check before you trust the number
First, check the bundles-per-square figure on the bundle label: 3 is standard, but heavier architectural shingles can take 4, and a wrong figure here moves the whole order — at 4 per square this roof needs 44 bundles, not 33. Second, measure the slope length, not the flat plan length: a pitched roof is longer on the slope, and the plan length under-orders by exactly the pitch factor. Third, judge the waste honestly: a simple gable roof fits 10%, but a roof with hips, valleys and dormers can want 15%, since every valley is cut shingles.
Worked example
40 ft long, 25 ft wide, 3 bundles per square, 10% waste. Roof area: 40 × 25 = 1000 sq ft. Squares: 1000 ÷ 100 = 10. Exact bundles: 10 × 3 = 30. With waste: 30 × 1.10 = 33 bundles. In practice that means ordering 33 bundles, and expecting the last bundles to go on the hips and valleys where the cutting happens. If the same roof used 4 bundles per square instead, the need would rise to 44 bundles with waste, but the roof covered would be identical.
Every branch, checked
With a 50 ft long roof instead of 40 ft, the area rises to 1250 sq ft and the need to 42 bundles with waste. With a 30 ft wide roof, the area rises to 1200 sq ft and the need to 40 bundles with waste. With 4 bundles per square, the area stays 1000 sq ft but the need rises to 44 bundles with waste. With 0% waste, the area stays 1000 sq ft and the need falls to 30 bundles. Area, bundle rate and waste each move the count on their own, so a wrong bundle rate is as costly as a wrong measurement.
The reverses, worked backwards
The length behind 33 bundles is 40 ft: at 32 ft the need is 27 bundles (8 squares, 800 sq ft roof, 10% waste); at 50 ft it is 42 bundles (12.5 squares, 1250 sq ft roof, 10% waste). The width behind 33 bundles is 25 ft: at 20 ft the need is 27 bundles (8 squares, 800 sq ft roof, 10% waste); at 30 ft it is 40 bundles (12 squares, 1200 sq ft roof, 10% waste). The waste behind 33 bundles is 10%: at 0% the need is 30 bundles; at 20% it is 36 bundles (10 squares, 1000 sq ft roof, 20% waste). Each reverse moves one input and holds the rest, so the step is exactly one dimension or one waste change.
What the defaults assume
The defaults assume a 40 ft by 25 ft rectangular roof slope, 3 bundles per square, and 10% cutting waste. They do not assume a second slope, a garage roof, starter strips, ridge caps, underlayment or flashing — a full house roof is usually two slopes measured separately, and ridge caps are bought by the linear foot, not by the bundle.
Who uses this
- A homeowner re-roofing a house: the 33-bundle order settles the merchant call before the first shingle is stripped.
- A DIY builder roofing a garage: the same maths on the garage slope alone gives the bundles, not a whole house.
- A roofer quoting a job: area, squares, bundles — the quote follows the same four steps, and the waste line shows the client why.
- A landlord budgeting a re-roof between tenants: the roof size off the plans, divided by 100, gives the shingle line on the refresh budget.
Accuracy & limitations
The arithmetic is exact for the inputs entered; the judgement is the bundles-per-square figure and the waste allowance. Real roofs slope, and the slope length is longer than the plan length; a roof measured flat under-orders. A cut-up roof wastes more than a simple gable, and a bundle label that promises more coverage than the shingles deliver under-orders the same way. Treat 33 bundles as the planning order for a simple rectangular slope at 3 bundles per square, and raise the waste to 15% for a roof with many valleys.
Cite this calculator
Bright Side Kit, “Shingle Calculator: 33 Bundles for a 40×25 ft Roof”, https://brightoolbox.com/shingle-calculator/, accessed 3 November 2026. Students and researchers: cite the calculator name, the page URL and the date you used it, and quote the defaults (40 ft × 25 ft roof, 3 bundles per square, 10% waste) so the 33-bundle result can be checked.
Frequently asked questions
How many bundles of shingles do I need for a 40×25 roof?
33 bundles at 3 per square with 10% waste. The roof is 1000 sq ft, or 10 squares; 10 × 3 = 30 bundles exact, and waste takes it to 33.
What is a square in roofing?
100 square feet of roof. Roofers price and order by the square, so a 1000 sq ft roof is 10 squares and a 1250 sq ft roof is 12.5 squares.
How many bundles are in a square of shingles?
Usually 3 for standard shingles, which is the figure this calculator uses. Heavier architectural shingles can take 4 bundles per square — check the bundle label before ordering.
How much waste should I allow for shingles?
10% for a simple gable roof, 15% or more for a roof with hips, valleys and dormers. Waste is the cutting, not spare stock: without it, the last valley comes up short.
Do I measure the roof flat or on the slope?
On the slope. A pitched roof is longer on the slope than on the plan, and the plan length under-orders. Measure each slope separately and add them for a full roof.
What else do I need besides the shingles?
Starter strips, ridge caps, underlayment and flashing, none of which are counted here. The square footage calculator gives the roof area itself, before squares and bundles are counted.