Roof square footage calculator: how big is your roof?

This roof square footage calculator turns your footprint and slope into real roof area. Pam's 1,500 sq ft ranch at 5/12 has about 1,625 sq ft of roof, or 16.3 squares.

Footprint

Measure the outside walls and add the overhang on each side. A 30 by 50 foot house with 1 foot eaves all around is 32 by 52, or 1,664 sq ft. Garages and porches under the same roof count.

Slope multiplier

A sloped roof is bigger than the ground below it. The multiplier is 1.083 at 5/12 and 1.118 at 6/12. Get yours from the roof pitch calculator.

Squares

Roofers count in squares. BuildFolio puts it plainly: one square is 100 sq ft. A 2,000 sq ft roof is 20 squares.

Waste

Shingles get cut at edges, hips and valleys. BuildFolio suggests 10% for a simple gable. We use 15% for hips and 20% for cut-up roofs with many valleys.

Shingles you'd need

Most shingles come three bundles to the square. Omni Calculator notes a bundle typically covers 33.3 sq ft. The shingle calculator works from roof area alone.

The square and waste figures come from BuildFolio's notes and the Omni shingle calculator.

How the roof square footage calculator works

It multiplies the footprint by the square root of rise squared plus 144, divided by 12. Then it divides by 100 for squares and adds waste. Nothing is sent anywhere while you type.

Worked examples

1. Pam: 1,500 sq ft at 5/12 with 10% waste. Roof 1,625 sq ft, order 17.9 squares, about 54 bundles.
2. A 2,000 sq ft footprint at 6/12 with 15% waste. Roof 2,236 sq ft, order 25.7 squares.
3. A 1,200 sq ft cabin at 12/12 with 10% waste. Roof 1,697 sq ft, order 18.7 squares.