Roofing Calculator
Estimate the size of your roof. Enter the length and width of the house, the overhang, and the roof pitch to see the roof area, the number of roofing squares, and how many bundles of shingles to buy.
Roof area
1,652.9 sq ft
Check the highlighted fields to see your result.
- In the other unit
- 153.6 m²
- Angle
- 26.6°
- Squares (100 sq ft)
- 16.53
- Shingle bundles
- 50
Results are estimates for information only and do not constitute financial, medical, or legal advice.
How it works
A sloped roof is larger than the floor it covers. The calculator takes the footprint of the house plus the overhang on each side and multiplies it by a pitch factor: the steeper the roof, the bigger the factor. Then it adds the extra you choose for waste.
The formulas
Roof area = (length + 2 × overhang) × (width + 2 × overhang) × pitch factor
Pitch factor = √(1 + (rise ÷ 12)²) · Squares = area ÷ 100
Worked example
A 40 × 30 ft house with a 1 ft overhang and a 6/12 roof, plus 10% for waste.
- Footprint with overhang: 42 × 32 = 1,344 sq ft.
- Pitch factor for 6/12: √(1 + 0.25) ≈ 1.118, so the roof is about 1,503 sq ft.
- With 10% extra: about 1,653 sq ft, or 16.5 squares and 50 bundles of shingles.
Frequently asked questions
What is a roofing square?
A square is 100 square feet of roof. Roofers price jobs and materials by the square. Standard asphalt shingles come in bundles, and three bundles cover one square.
Does the shape of the roof matter?
For simple gable and hip roofs with the same pitch on every side, the area is the footprint times the pitch factor, which is what this calculator uses. Dormers, valleys, and different pitches add area and waste, so complex roofs need a closer measurement.
How much extra should I order?
About 10% for a simple gable roof and 15% or more for roofs with many valleys, hips, or dormers, to cover cuts, starter rows, and ridge caps.