Roofing squares calculator
Type the footprint and the pitch. The calculator gives the flat area, the pitch factor, the sloped area and the squares of roofing.
Squares of roofing = footprint length × width × pitch factor ÷ 100. A square is 100 square feet of roof surface.
How the math works
The footprint is what you see from above: the flat area inside the eaves and rakes. Roofing covers the slope, which is longer than the footprint in the direction the roof climbs. The pitch factor is how much longer: the square root of 1 plus the pitch squared, with the pitch written as rise over 12. At 6/12 the factor is 1.118, so every flat square foot is 1.118 square feet of roofing.
| Step | Example, 40 × 30 ft at 6/12 |
|---|---|
| Flat area | 40 × 30 = 1,200 sq ft |
| Pitch factor at 6/12 | 1.118 |
| Sloped area | 1,200 × 1.118 = 1,342 sq ft |
| Squares | 1,342 ÷ 100 = 13.4 squares |
Include the overhangs in the footprint. A 40 by 30 foot house with 1 foot eaves on all four sides has a 42 by 32 foot roof footprint.
Where the calculator stops
This figure is right for one roof at one pitch, gable or hip. It does not know about a 4/12 porch under an 8/12 main roof, a dormer, a two-story section stepping down to a garage, or a valley that cuts a facet into two pieces that each waste a cut. Every one of those is a separate facet with its own area, and the pieces you buy come from how the courses or panels land on each facet.
Squares to buy are not squares of area plus a waste guess. All Roof Pricer lays every course of shingles or tile and every metal panel on each facet, counts the whole pieces and the cut pieces, and adds them up. The waste is whatever the roof actually wastes. How the layout works.
Questions
What is a roofing square?
A roofing square is 100 square feet of roof surface. Roofing material is sold and roofing labor is quoted by the square. A roof with 2,400 square feet of sloped surface is 24 squares.
How do I calculate roofing squares from a house footprint?
Multiply the footprint length by the width to get the flat area, multiply by the pitch factor for the roof pitch to get the sloped area, then divide by 100. A 40 by 30 foot footprint at 6/12 is 1,200 flat square feet, times 1.118, equals 1,342 sloped square feet, or 13.4 squares.
How much waste should I add to the squares?
The usual rule of thumb is 10 percent for a simple gable and 15 percent or more for a hip roof or one with valleys and dormers. The rule exists because nobody wants to lay out every cut by hand. All Roof Pricer lays every course or panel on every facet and counts the cut pieces, so the squares to buy come from the actual layout instead of a guess.
Does the calculator work for a hip roof?
For a plain hip roof with one pitch, yes: the sloped area of a hip roof equals the footprint times the pitch factor, the same as a gable of the same pitch. Roofs with more than one pitch, dormers, or sections at different heights need each facet figured on its own.