Roofing Calculator
Estimate your roof area, roofing squares, and shingle bundles from the building footprint and roof pitch.
Results are estimates. Complex roofs with many hips, valleys, and dormers need extra material. Measure on the roof where it is safe to do so, and confirm with a roofer for a full job.
How to Measure a Roof
Roofing is ordered by the square — 100 square feet of roof surface. You can get the surface area two ways.
Footprint plus pitch
Measure the building's footprint length and width at ground level, then choose the roof pitch. The calculator multiplies the footprint by a pitch factor to estimate the sloped surface area — handy when you can't get on the roof.
Direct roof area
If you have measured the actual roof planes, switch to the Roof area tab and enter the total surface area in square feet.
Pitch
Pitch is the rise over a 12-inch run. A 6/12 roof rises 6 inches per foot. The steeper the pitch, the more surface area above the same footprint.
Common Mistakes to Avoid
- Using the footprint as the roof area. A sloped roof always has more surface than the floor below it — apply the pitch factor.
- Too little waste. Hips, valleys, and dormers all need cut shingles. Use 10-15% waste, not zero.
- Forgetting starter and ridge. This estimate covers the field shingles; order starter strip and ridge cap separately.
- Skipping underlayment and flashing. Bundles aren't the whole job — plan felt or synthetic underlayment, drip edge, and flashing too.
Frequently Asked Questions
It takes 3 bundles to cover one square (100 sq ft). Work out your roof area, divide by 100 for squares, and multiply by 3 for bundles.
A roofing square is 100 square feet of roof surface. Roofers price and order by the square, so a 2,000 sq ft roof is 20 squares.
Measure the building footprint, then multiply by a pitch factor for the slope — a 6/12 pitch is about 1.12. The calculator applies the factor when you pick a pitch.
About 10% for a simple gable roof, and up to 15% for roofs with many hips, valleys, and dormers.
Three bundles per square is standard for architectural and most 3-tab asphalt shingles. Heavier shingles can take four or more.