Multiply your house length by your house width to get the area. (For example, 40 feet x 30 feet = 1,200 square feet.) Next, multiply the area by your roof’s pitch. (1,200 x 1.05 = 1,260 square feet.)
Calculate the exact roof area
Follow these steps to figure out the exact area of your roof:
- Take your pitch number and divide it by 12. For example, if your pitch is 4 in 12, divide 4 by 12. The answer will be 1/3.
- Next, square your outcome. In our example, 1/3 squared will yield 1/9.
- Add 1 to your result: 1/9 + 1 = 10/9
- Calculate the square root of your new number: sqrt(10/9) = 1.05.
- Measure the length and width of your house (including overhangs).
- Multiply length x width for the area (e.g., 40 x 20 = 1,200 sq. ft.).
- Multiply area by pitch factor to get roof area: 1,200 x 1.05 = 1,260 sq. ft.
To allow for ridges, hips, and waste, add 10% for gable roofs or 17% for cottage roofs. Follow Us!
Final values: 1,386 sq. ft. (gable) or 1,474 sq. ft. (cottage). Get to know more about us!
Know Your Roof Type
There are three main types of roofs common in the Dallas area:
- Shed roofs: simple square or rectangle, easy to measure.
- Gable roofs: sloped on two sides, meet in a triangle.
- Hip roofs: four sloped triangles towards a peak, more complex to calculate.
Get a Friend, Get On the Roof, and Measure Your Roof
Use a tape measure to get dimensions:
- For a 12′ x 12′ shed: 144 sq. ft. to be shingled.
- Gable roof: 15′ x 30′ planes x2 = 900 sq. ft. total.
- Hip roof: use trapezoid and triangle formulas for each side.
Roofing Materials
The goal of precise roof measurement is to ensure enough material is ordered for shingles, metal, or other roof types.
Shingles
Sold in bundles; bundles per square vary by brand. Always compare by square, not bundle.
Metal Roofing
Sold in sheets or panels. Divide roof width by panel coverage width to determine quantity.
Other Roofing Materials
Don’t forget leak barriers, deck protection, drip/rake edge, ridge vents, and hip/ridge caps in your estimate.