Free Roofing Calculator: Squares, Bundles and More
Enter the house footprint, the pitch and the overhang. The calculator finds the sloped roof area and the squares, then the shingles and the rest of the material list. These are the same rules LaraKey’s takeoff calculator uses.
Roofing materials
Roof pitch multipliers
Multiply the flat footprint (with overhangs) by the factor to get the sloped roof area.
| Pitch | Multiplier | 1,000 sq ft footprint becomes |
|---|---|---|
| 2/12 | 1.014 | 1,014 sq ft |
| 3/12 | 1.031 | 1,031 sq ft |
| 4/12 | 1.054 | 1,054 sq ft |
| 5/12 | 1.083 | 1,083 sq ft |
| 6/12 | 1.118 | 1,118 sq ft |
| 7/12 | 1.158 | 1,158 sq ft |
| 8/12 | 1.202 | 1,202 sq ft |
| 9/12 | 1.250 | 1,250 sq ft |
| 10/12 | 1.302 | 1,302 sq ft |
| 12/12 | 1.414 | 1,414 sq ft |
Estimates only. Measure on site and check with your supplier before you order.
How to calculate a roof
Plan area = (Length + 2 × overhang) × (Width + 2 × overhang)
Pitch multiplier = √(12² + rise²) ÷ 12
Roof area = Plan area × Pitch multiplier. Squares = Roof area ÷ 100.
Shingle bundles = Squares × 3 + waste (about 10% gable, 15% hip)
Underlayment = Roof area ÷ 1,000 sq ft per roll + 10%
Ice & water shield = Eaves × 3 ft ÷ 200 sq ft per roll + 10%
Drip edge = (Eaves + Rakes) ÷ 10 ft + 5%. Starter = (Eaves + Rakes) ÷ 105 ft per bundle + 5%. Ridge cap = (Ridge + Hips) ÷ 25 ft per bundle + 5%.
Examples
A 40 × 30 ft gable house, 6/12
With 12 in overhangs the plan is 42 × 32 = 1,344 sq ft. × 1.118 = 1,503 sq ft = 15.0 squares. Shingles: 15.0 × 3 × 1.1 = 50 bundles. Underlayment: 2 rolls.
The same house as a hip roof
Same 15.0 squares, but at 15% waste: 15.0 × 3 × 1.15 = 52 bundles. No rakes, so less drip edge, and the hips add ridge cap.
Roofing Calculator: common questions
What is a roofing square?
100 square feet of roof surface. Shingles are usually sold as 3 bundles per square.
How do I find my roof pitch?
Pitch is how many inches the roof rises for every 12 inches across. Hold a level out 12 inches from the roof and measure straight up to the roof surface.
What is a pitch multiplier?
The number you multiply the flat footprint by to get the sloped roof area. A 6/12 roof is 1.118, so a 1,000 sq ft footprint has about 1,118 sq ft of roof.
How much waste should I add for shingles?
About 10% on a simple gable roof and 15% on a hip roof, more with lots of valleys and dormers.
Does this work for complicated roofs?
It assumes one simple gable or hip roof. For dormers, valleys and additions, measure each section and add them up.
How many bundles of shingles cover a square?
Most architectural shingles take 3 bundles per square. Check the wrapper; some heavy shingles take 4 or 5.
Do I need ice and water shield?
Many codes require it at the eaves in cold climates, and it’s smart in valleys everywhere. The calculator figures a 3 ft strip along the eaves.
Are these numbers exact?
They’re estimates. Measure the roof and confirm with your supplier before you order.
Talk to a person who knows remodeling.
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