Roof square footage calculator
Roof square footage calculator
Estimate roof area, roofing squares and shingle bundles from the building size and pitch. Know the address? Measure the actual roof from LiDAR instead.
Plan area = (length + 2 × overhang) × (width + 2 × overhang). Roof area = plan area × slope factor. Assumes one pitch across the whole roof.
How to measure roof square footage
- Find the plan area. Measure the outside walls and add the overhang on each side, or use the footprint from a property record.
- Find the pitch. Rise in inches per 12 inches of run — from a pitch gauge, the attic rafters, or by address from LiDAR.
- Apply the slope factor. Multiply the plan area by √(1 + (pitch/12)²) — see the roof pitch chart.
- Convert to squares. Divide by 100, add waste, and multiply by 3 for shingle bundles. Then price it in the roofing cost calculator.
Roof square footage questions
How do I calculate the square footage of a roof?
Take the building footprint plus the overhang on every side, then multiply by the slope factor for the pitch: √(1 + (pitch/12)²). A 40 × 30 ft house with 1 ft overhangs is 42 × 32 = 1,344 sq ft in plan; at 6/12 (factor 1.118) that is about 1,503 sq ft of roof.
How many squares is my roof?
One roofing square is 100 sq ft of roof surface. Divide the roof area by 100: a 2,400 sq ft roof is 24 squares. Order extra for waste — about 10% on a simple gable, 15% or more on hip roofs with valleys.
How many bundles of shingles do I need?
Most architectural and 3-tab shingles come three bundles to a square, so bundles = squares to order × 3. Starter strip and ridge cap are counted separately by length.
Is a footprint-based estimate accurate?
It is a good planning number for simple roofs. Dormers, multiple pitches, porches and complex hips change the real area. For a measurement from the actual roof, enter the address — we read the pitch from aerial LiDAR.