Roofing Calculator
Enter your house size and roof pitch to get the true sloped roof area, squares and shingle bundles. You also get a full shopping list: underlayment, drip edge, ice and water shield, ridge cap, starter strip and nails, with waste included.
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Roof area = footprint (including overhangs) × pitch factor. Divide by 100 for squares, add 10–15% waste, then multiply by 3 for shingle bundles. A 40 × 30 ft house with 12 in overhangs and a 6/12 gable roof has about 1,503 sq ft of roof. That is 16.5 squares with waste, or 50 bundles of architectural shingles.
How to use this roofing calculator
- Measure the house, not the roof. Length and width of the footprint are safe to measure from the ground or from plans. Add your overhang (eave and rake projection), usually 12–24 in.
- Pick the pitch. Pitch is inches of rise per 12 inches of run. Most US homes are 4/12 to 8/12. Not sure? Use the roof pitch calculator.
- Choose gable or hip. Roof area is the same for both at the same pitch, but edges, ridge length and waste are different.
- Already have the roof area? Switch to Measured roof area and enter it from a roof report or drone measurement.
- Read your list: squares, bundles, cost, and every accessory you need to order with them.
How to calculate roofing squares
Roofing is sold by the square, which is 100 sq ft of roof surface. A sloped roof has more surface than the ground it covers, so multiply the footprint by a pitch factor.
| Pitch | Angle | Pitch factor | 1,000 sq ft footprint becomes |
|---|---|---|---|
| 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° | 1.250 | 1,250 sq ft |
| 10/12 | 39.8° | 1.302 | 1,302 sq ft |
| 12/12 | 45.0° | 1.414 | 1,414 sq ft |
The same factor applies to gable and hip roofs of the same pitch. A hip roof does not have more surface, it just has more cutting, which is why it needs more waste.
How many bundles of shingles per square?
| Shingle type | Bundles per square | Coverage per bundle | Typical weight per square |
|---|---|---|---|
| 3-tab | 3 | ~33.3 sq ft | ~200–240 lb |
| Architectural (dimensional) | 3 | ~33.3 sq ft | ~240–300 lb |
| Designer / luxury | 4–5 | ~20–25 sq ft | ~350 lb and up |
Coverage varies by brand, so check the wrapper before ordering. Weight matters too. A 30-square roof of architectural shingles is roughly 4 tons on the deck, so arrange a rooftop drop with your supplier.
How much waste to add
- Simple gable roof: 10%Straight cuts at the rakes only. Starter and ridge offcuts account for most of the loss.
- Hip roof: 15%Every hip line needs angled cuts on both sides, and those offcuts are rarely reusable.
- Valleys, dormers, skylights: 15–20%Each extra feature adds cutting. Complex roofs on steep pitches sit at the top of the range.
Everything else you need besides shingles
- UnderlaymentSynthetic rolls usually cover 10 squares, #15 felt about 4. Check local code for the required type and overlap.
- Ice and water shieldSelf-adhered membrane along eaves (and in valleys) in cold climates. The calculator assumes one 3 ft course along every eave.
- Drip edgeMetal edge along eaves and rakes, sold in 10 ft pieces. The count includes 5% for laps.
- Starter stripFirst course along eaves and rakes. One bundle covers roughly 100–120 linear feet.
- Ridge capCovers ridges and hips. Coverage varies widely by product (about 20–35 lf per bundle). We assume 25 lf to be safe.
- NailsAbout 4 nails per shingle (6 in high-wind zones), which works out to roughly 2–3 lb of 1¼ in coil nails per square.
For detailed counts of each item, use the underlayment, ridge cap and flashing, and gutter and downspout calculators.
Minimum roof pitch by material
| Roofing | Minimum pitch | Notes |
|---|---|---|
| Asphalt shingles | 2/12 | 2/12 to under 4/12 needs double underlayment; 4/12+ is standard |
| Standing seam metal | about 1/4–12 to 3/12 | Depends on panel and seam type |
| Exposed-fastener metal panels | 3/12 | Lower slopes risk leaks at fasteners |
| Clay or concrete tile | 2.5/12–4/12 | Check manufacturer and code |
Always follow the shingle manufacturer’s instructions and your local building code. They override these general figures.
Worked example
- House 40 × 30 ft, 12 in overhang
- 42 × 32 = 1,344 sq ft
- 6/12 pitch factor
- 1,344 × 1.118 = 1,503 sq ft
- Add 10% waste
- 1,653 sq ft = 16.5 squares
- Shingles (3 bundles per square)
- 50 bundles
- Underlayment (10-square rolls)
- 2 rolls
- Drip edge (84 ft eaves + 72 ft rakes)
- 17 pieces
All 6 roofing calculators
Specialist roofing calculators for every part of the job.
Frequently asked questions
How do I calculate how many squares my roof is?
Multiply length × width including overhangs, then by the pitch factor (1.118 for 6/12). Divide by 100 for squares and add 10–15% waste.
How many bundles of shingles are in a square?
Three for most architectural and 3-tab shingles, each covering about 33.3 sq ft. Heavier designer shingles often take four. Check the wrapper.
How many bundles of shingles do I need for 2,000 sq ft?
2,000 sq ft of roof surface is 20 squares. That is 60 bundles, or 66 with 10% waste.
How much waste should I add for shingles?
About 10% for a simple gable roof and 15% for hip roofs. Allow 15–20% for valleys, dormers and skylights.
What is a roof pitch factor?
It converts footprint area into sloped area: √(1 + (rise ÷ 12)²). 4/12 is 1.054, 6/12 is 1.118, 8/12 is 1.202 and 12/12 is 1.414.
How many rolls of underlayment do I need?
Divide roof area including waste by roll coverage. Synthetic rolls are usually 10 squares (1,000 sq ft) and #15 felt about 4 squares.
What this calculator assumes
- Uniform pitch on every slope. For mixed pitches, calculate each section with Measured roof area.
- Hip roofs are treated as a full hip with a ridge of length minus width.
- Bundle and roll coverages are typical US values. Check your product’s label.
- Prices are material estimates only, before tax and delivery, and exclude labor and tear-off.