Roofing calculator
This roofing calculator finds your roof’s surface area from the house footprint and roof pitch, then converts it to roofing squares and bundles of shingles, with extra for waste.
- Roof area from footprint and pitch
- Squares and 3-bundle-per-square shingles
- Pitch multiplier chart from 1/12 to 18/12
Last updated
How to use the roofing calculator
- Measure the house footprint, including the roof overhangs, or take it from your plans. For an L-shaped house, total the sections in the square footage calculator first.
- Pick the roof pitch: the inches the roof rises for every 12 inches it runs.
- Set the waste. 10 percent suits a simple gable roof; hips, valleys and dormers need more.
- Read the roof area, the number of squares and the bundles of shingles. Check the bundles per square printed on your shingle wrapper.
How roof area is calculated
A sloped roof has more surface than the flat footprint under it. The pitch multiplier is the length of the sloped rafter for every foot of level run:
pitch multiplier = √(1 + (rise ÷ 12)²)
roof area = footprint (with overhangs) × pitch multiplier
squares = roof area × (1 + waste) ÷ 100, and bundles = squares × bundles per square
This works for gable and hip roofs alike, as long as every plane has the same pitch. A roofing square is 100 square feet. GAF notes that most standard asphalt shingles, both 3-tab and architectural, come three bundles to the square, while some heavier specialty shingles take four or five.
Worked example
A house 40 × 30 ft including overhangs, with a 6/12 roof and 10% waste.
- Footprint: 40 × 30 = 1,200 sq ft.
- Multiplier for 6/12: √(1 + 0.5²) = 1.118.
- Roof area: 1,200 × 1.118 = 1,341.6 sq ft.
- With 10% waste: 1,475.8 sq ft, which is 14.76 squares.
- Bundles: 14.76 × 3 = 44.3, so 45 bundles.
Starter strip, hip and ridge caps, underlayment and drip edge are ordered separately.
Roof pitch multiplier chart
Multiply the footprint by the factor for your pitch. The angle is the slope in degrees.
| Pitch | Multiplier | Angle | Roof sq ft per 1,000 sq ft footprint |
|---|---|---|---|
| 1/12 | 1.003 | 4.8° | 1,003 |
| 2/12 | 1.014 | 9.5° | 1,014 |
| 3/12 | 1.031 | 14.0° | 1,031 |
| 4/12 | 1.054 | 18.4° | 1,054 |
| 5/12 | 1.083 | 22.6° | 1,083 |
| 6/12 | 1.118 | 26.6° | 1,118 |
| 7/12 | 1.158 | 30.3° | 1,158 |
| 8/12 | 1.202 | 33.7° | 1,202 |
| 9/12 | 1.250 | 36.9° | 1,250 |
| 10/12 | 1.302 | 39.8° | 1,302 |
| 11/12 | 1.357 | 42.5° | 1,357 |
| 12/12 | 1.414 | 45.0° | 1,414 |
| 14/12 | 1.537 | 49.4° | 1,537 |
| 16/12 | 1.667 | 53.1° | 1,667 |
| 18/12 | 1.803 | 56.3° | 1,803 |
How to find your roof pitch
- From the attic or a gable end: hold a level horizontal against a rafter, mark 12 inches along it, and measure straight up from that mark to the underside of the rafter. That number is the rise: 6 inches means 6/12.
- From the angle: rise = 12 × tan(angle). A 30° roof is about 7/12.
- Stay off steep roofs. Measure from a ladder at the eave or from inside, not by walking a roof you are not equipped for.
Common questions
How do I calculate how many squares my roof is?
Multiply the footprint (with overhangs) by the pitch multiplier, then divide by 100. A 1,200 sq ft footprint with a 6/12 roof is 1,200 × 1.118 = 1,342 sq ft, or 13.4 squares before waste.
How many bundles of shingles are in a square?
Most standard asphalt shingles come 3 bundles to a square (100 sq ft), so each bundle covers about 33.3 sq ft. GAF notes some specialty shingles take 4 or 5 bundles per square, so check the wrapper.
How many bundles of shingles do I need for a 1,000 sq ft roof?
1,000 sq ft of roof surface is 10 squares, or 30 bundles. With 10% waste it is 11 squares, or 33 bundles.
What is the multiplier for a 6/12 pitch roof?
1.118. The roof surface is 11.8% larger than the flat area under it. For 4/12 it is 1.054, for 8/12 1.202, and for 12/12 1.414.
How much waste should I add for roofing?
About 10 percent for a simple gable roof is a common starting point. Hips, valleys, dormers and short runs mean more cutting, so add more for a complex roof, and follow your roofer’s takeoff if you have one.
How do I convert roof pitch to degrees?
Divide the rise by 12 and take the inverse tangent. 6/12 is arctan(0.5) = 26.6°, and 12/12 is 45°.
Sources
- GAF: How many bundles of shingles are in a square. A roofing square is 100 sq ft; most standard asphalt shingles come three bundles per square, some specialty lines four or five. Last checked 28 October 2026
See the methodology page for how YardageHQ builds and checks its calculators.