How to Calculate the Square Footage of a Metal Roof

Measuring the surface of a roof -- whether metal, tile or thatch -- requires a similar approach. Gain safe access to the roof, be aware of dangers working above the ground and measure accurately. The square footage of a metal roof is simply its surface area measured in square feet, so the measuring and calculations are straightforward.

Tape measure

Instructions

- 1
  Divide the roof area into rectangles and, if necessary, triangles too. While it's difficult to calculate the square footage of irregular shapes, by breaking them into several regular areas, the calculations become easier. For example, a roof with a central ridge and two sloping sides can be divided into two rectangles, while a dormer roof connected to a pitched roof can be divided into a rectangle and a triangular section where the dormer butts against the pitched roof.
- 2
  Measure, in feet, the length and width of each of the regular shapes. Record the dimensions for later use. Don't overlap the separate areas or leave gaps between them.
- 3
  Calculate the square footage of each rectangle and triangle using these formulas:
  Rectangle: area = width x length
  Triangle: area = (width x length) / 2
  
  For example, a rectangular roof section that's 30 feet long and 20 feet wide has a square footage of 600 square feet (20 times 30 equals 600). Likewise, a triangular roof area that's 20 feet wide and 30 feet high has a square footage of 300 square feet (20 times 30 divided by 2 equals 300).
- 4
  Add together all separate areas to determine the total area of the metal roof. For example, a roof consisting of a rectangle covering 600 square feet and triangle covering 300 square feet has a total square footage of 900 square feet.

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