Roofing Calculator
Roof area from the footprint and pitch, in square feet, square metres and roofing squares, plus shingle bundles.
Your roof
Filled in with example values. Replace them with your own.
Roof seen from above
How many units the roof rises for every 12 units across, for example 6 in 12.
Extras
Cuts at hips, valleys and edges are partly wasted. On by default; your roofing supplier or the product guide can suggest a figure.
Enter how many bundles cover one square (100 ft²). It is printed on the package and differs by product.
Results update as you type.
Result
Roof area: 1,475.8 ft² (including 10% extra)
Roof area to cover
1,475.8square feet
- Roofing squares1 square = 100 ft²
- 14.76
- Roof areaBefore extra
- 1,341.6 ft²
- Area from above
- 1,200 ft²
- Pitch
- 6/12 (26.6°)
- Pitch factorSloped area ÷ flat area
- 1.12
How it’s calculated
Area from above
40 ft × 30 ft = 1,200 ft²
Pitch factor
√(1 + (6 ÷ 12)²) = 1.12
Roof area
1,200 ft² × 1.12 = 1,341.6 ft²
Plus 10% extra
1,341.6 ft² × 1.1 = 1,475.8 ft²
Squares
1,475.8 ft² ÷ 100 = 14.76
How the roofing calculator works
Measure the roof as seen from above, including the overhangs at the eaves and gables, and enter its pitch as a rise in 12 or as an angle. The calculator multiplies the area from above by the pitch factor to get the sloped roof area, adds a percentage for waste and converts the result to roofing squares. If you enter how many bundles cover one square, it counts bundles too.
The formula
Pitch factor = √(1 + (Rise ÷ 12)²) = 1 ÷ cos(Angle)
Roof area = Length × Width × Pitch factor
Squares = Roof area in ft² × (1 + Extra % ÷ 100) ÷ 100
Bundles = Squares × Bundles per square, rounded up
Worked example
A house measures 40 × 30 ft from above including overhangs, with a 6 in 12pitch and 10% extra:
- Area from above: 40 × 30 = 1,200 ft²
- Pitch factor: √(1 + 0.5²) = √1.25 = 1.1180
- Roof area: 1,200 × 1.1180 = 1,341.6 ft²
- With 10% extra: 1,341.6 × 1.1 = 1,475.8 ft², which is 14.76 squares
Suppose the shingles you choose need 3 bundles per square. This is an example only; use the figure on the package. 14.76 × 3 = 44.27, so you would buy 45 bundles.
Units, assumptions and limitations
- The roof is a rectangle from above, and all its planes share one pitch.
- Dormers, chimneys, skylights and roofs with several pitches are not handled. Calculate those parts separately.
- Ridge caps, starter strips, underlayment, flashing and fixings are not included.
- No bundles per square are assumed. Products differ, so enter the figure from the package.
- Whether a roofing material suits a given pitch is set by the manufacturer and local building rules. This calculator does not check it.
Frequently asked questions
What does a pitch of 6 in 12 mean?
The roof rises 6 units for every 12 units it runs horizontally, in any unit: 6 inches per foot, or 50 cm per 100 cm. As an angle it is about 26.6°. The calculator converts between the two.
What is a roofing square?
A unit used in the US roofing trade: one square covers 100 square feet of roof. Shingles and other materials are often priced and packaged by the square.
Why measure the roof from above instead of climbing on it?
Every roof plane with the same pitch is longer than its shadow by the same factor, √(1 + (rise ÷ 12)²). So the area from above, which you can measure from the ground or a plan, times that factor gives the sloped area exactly.
Does it work for a hip roof?
Yes, as long as every plane has the same pitch. The pitch factor is the same for each plane, so the total does not depend on how the roof is divided into planes. Roofs with different pitches need each part calculated separately.
How many bundles of shingles are in a square?
It depends on the product, so check the package. Enter the figure from the label and the calculator multiplies it by the number of squares and rounds up.