Roofing squares & shingle calculator
Enter your roof's footprint and its pitch and this gives you the roof area in squares, the shingle bundles, and the sheathing and underlayment to order. It runs the same area math as the CutOnce app, which also does the ridge, hip, starter, and drip-edge takeoffs.
Updated
The short answer
Roofing is sold in squares, and one square covers 100 sq ft of roof. To get your squares, take the roof's flat footprint area, multiply by the pitch factor for its slope, divide by 100, then add 10 to 15% for waste. A standard 3-tab or architectural shingle runs 3 bundles to the square.
Footprint is the flat plan outline; the pitch factor scales it up to the sloped roof. One square is 100 sq ft. Counts round up to the whole bundle, sheet, and roll.
- Roof surface area
- 1,342 sq ft
- Squares (before waste)
- 13.42
- Shingle bundles
- 45
- 4x8 sheathing sheets
- 47
- Underlayment rolls
- 4
What a roofing square is
A square is 100 sq ft of finished roof, the unit every shingle, underlayment, and labor price is quoted in. It has nothing to do with the shape of the roof. The catch is that a square is measured on the slope, not on the ground: a roof always has more surface than the footprint it covers, because the slope stretches it. That stretch is the pitch factor, and skipping it is the single most common way a roof order comes up short.
A worked example
A 40 by 30 ft footprint (1,200 sq ft on the ground) at a 6/12 pitch, with 10% waste and 3-bundle shingles. Here is the full takeoff and where each number comes from.
| Footprint area | 1,200 sq ft | 40 x 30, flat on plan |
| Pitch factor | 1.1180 | sqrt(1 + (6/12) squared) for a 6/12 slope |
| Roof surface area | 1,342 sq ft | footprint x pitch factor |
| Squares (with waste) | 14.8 | roof area / 100, plus 10% waste |
| Shingle bundles | 45 | squares x 3 bundles, plus waste, rounded up |
| Sheathing sheets | 47 | roof area / 32 sq ft per 4x8, rounded up |
| Underlayment rolls | 4 | roof area / 400 sq ft per roll, rounded up |
The pitch factor, by slope
This is the multiplier from flat footprint to sloped roof area. Multiply your ground-level footprint by the factor for your pitch, then divide by 100 for squares. A steeper roof has more surface, so it takes more shingles for the same floor plan.
| Pitch | Pitch factor | Squares per 1,000 sq ft footprint |
|---|---|---|
| 3/12 | 1.031 | 10.3 |
| 4/12 | 1.054 | 10.5 |
| 6/12 | 1.118 | 11.2 |
| 8/12 | 1.202 | 12.0 |
| 12/12 | 1.414 | 14.1 |
What this page does and what the app adds
This page sizes the area materials: squares, shingle bundles, 4x8 sheathing, and underlayment. Those come straight from the roof area, so a footprint and a pitch are all it needs. The linear materials, hip and ridge cap, starter strip, and drip edge, depend on how long each ridge, hip, eave, and rake actually is, which comes from the roof's plan shape. The app derives those once you tell it the roof type and dimensions, and it prints the whole takeoff. This page does not guess them, because a number that is only sometimes right is worse than no number on an order sheet.
Common questions
- How many squares is a 2,000 sq ft roof?
- If 2,000 sq ft is the actual roof surface, that is 20 squares, because a square is 100 sq ft. If 2,000 sq ft is the house's footprint, you have to multiply by the pitch factor first: at a 6/12 pitch that is about 22.4 squares, and at 12/12 it is about 28.3. Always confirm whether the number you were given is the footprint or the roof surface.
- How many bundles of shingles are in a square?
- Three, for most 3-tab and architectural shingles, so a bundle covers about 33 sq ft. Heavier designer and some architectural lines run 4 or even 5 bundles to the square; the wrapper states the coverage. The calculator lets you set bundles per square so the count matches the exact shingle you are buying.
- Do I measure the roof or the ground?
- You can start from either. Measuring the roof surface directly (off the shingles or an aerial report) gives you the area with the pitch already in it, so divide by 100 and you have squares. Measuring the footprint on the ground is easier and safer, but then you must apply the pitch factor to get the true sloped area. This calculator does the footprint-plus-pitch path.
- How much waste should I add?
- Ten percent is the common starting point for a simple gable roof. Go to 15% or more for a cut-up roof with lots of hips, valleys, and dormers, where every diagonal cut throws away part of a shingle. Steep-slope and complex roofs waste more; a plain rectangle wastes less. The calculator applies whatever waste percent you set to the shingles, sheathing, and underlayment together.
- Does a steeper roof really need more shingles?
- Yes, for the same footprint. The floor plan does not change, but the roof surface over it grows with the slope. A 12/12 roof has about 1.41 times the surface of the flat footprint, versus 1.12 for a 6/12, so the same house takes noticeably more material and labor under a steep roof. That is exactly what the pitch factor captures.
The whole roof takeoff, not just the field
CutOnce sizes the shingles, sheathing, and underlayment like this page, then adds the ridge and hip cap, starter, and drip edge from the roof's real geometry, and lays out the rafters and hips while it is at it.
Free to download, with a 7-day trial of everything. The web calculator is the teaser; the app prints the order sheet.
See also