Roofing & Exterior
Roofing Calculator
Estimate your roof area and roofing materials. Enter the house footprint and roof pitch, or measure each roof plane, and this roofing calculator gives the roof square footage, roofing squares, shingle bundles, underlayment, drip edge and ridge cap, with an optional material cost.
Result
Enter your measurements and press Calculate. What to buy, the working and the cost will appear here.
How to use the roofing calculator
- Choose how to measure. For a simple gable or hip roof over a rectangle, use the footprint. For anything else, measure each roof plane on the roof itself.
- Enter the footprint, overhang and pitch, or each plane’s length along the eave and width up the slope.
- Set the waste: 10% for gables, 15% for hips, valleys and dormers.
- Check bundles per square on the shingle wrapper, choose the underlayment, add prices and press Calculate.
How roof area is calculated
roof area = (length + 2 × overhang) × (width + 2 × overhang) × pitch factor
squares = roof area × (1 + waste) ÷ 100
The pitch factor converts flat footprint area into sloped roof area. A 6:12 roof has a factor of 1.118, so a 1,000 ft² footprint has about 1,118 ft² of roof.
Worked example: a 40 × 28 ft house
A 40 × 28 ft house with a 12 in overhang and a 6:12 gable roof, shingles at $38 a bundle and synthetic underlayment at $95 a roll:
- Footprint with overhang: 42 ft × 30 ft = 1,260 ft²
- Roof area: 1,260 ft² × pitch factor 1.118 = 1,408.72 ft²
- Squares: 1,408.72 ft² × 1.1 ÷ 100 ft² = 15.5 squares
- Bundles: 15.5 × 3 → 47
Roof area: 1,408.72 ft²; Roofing squares: 15.5 squares; Shingle bundles: 47; Underlayment: 2 rolls; Material cost: $1,976.00. Open this example in the calculator.
Roof pitch factors
| Pitch | Angle | Pitch factor |
|---|---|---|
| 1:12 | 4.8° | 1.003 |
| 2:12 | 9.5° | 1.014 |
| 3:12 | 14° | 1.031 |
| 4:12 | 18.4° | 1.054 |
| 5:12 | 22.6° | 1.083 |
| 6:12 | 26.6° | 1.118 |
| 7:12 | 30.3° | 1.158 |
| 8:12 | 33.7° | 1.202 |
| 9:12 | 36.9° | 1.25 |
| 10:12 | 39.8° | 1.302 |
| 11:12 | 42.5° | 1.357 |
| 12:12 | 45° | 1.414 |
Don’t know the pitch? The roof pitch calculator works it out from a rise and run measured with a level.
What is a roofing square?
Roofing is priced and ordered by the square: 100 ft² of roof. Most asphalt shingles come three bundles to a square, so a 25-square roof needs 75 bundles plus waste. Heavier architectural shingles can be four or five bundles per square.
Other roofing materials
- Underlayment goes over the whole deck; synthetic rolls commonly cover 10 squares, #15 felt about 4.
- Ice and water shield is required along eaves and in valleys in many cold climates; check your code.
- Drip edge runs along eaves and rakes, in 10 ft lengths.
- Starter strip along the eaves (and often rakes), and hip and ridge cap along every hip and the ridge.
- Nails, vents, flashing and pipe boots depend on the roof; your supplier can help with the list.
Assumptions and limitations
- Footprint mode assumes a single-pitch gable or hip roof over a rectangle. Complex roofs should be measured plane by plane.
- Ridge length for a hip roof is estimated from the footprint and pitch.
- This is a material estimate; it does not cover ventilation, structure or code requirements.
Roofing questions
How do I calculate roofing squares?
Find the roof area in square feet (footprint × pitch factor, or the sum of each plane), add 10–15% for waste, and divide by 100.
How many bundles of shingles are in a square?
Usually three, covering 33.3 ft² each. Some architectural shingles are four or five bundles per square.
How big is a 2,000 square foot house roof?
On a single-story house with a 6:12 pitch and 1 ft overhangs, roughly 2,400–2,500 ft² of roof, or about 27 squares with 10% waste. Two-story houses have a smaller roof for the same floor area.
Formulas, unit conversions and default values are explained on our methodology page. Results are estimates; check manufacturer data and local codes before you buy or build.