Blueprint takeoff

How to Measure a Roof from Blueprints

Having only a blueprint for a new home doesn’t mean that a roofing contractor must put aside their high-tech roof measurement and estimating application and pull out the ol’ tri-ruler.

An app certainly can make it a lot easier to produce a roofing report and detailed cost estimate faster than you can say “win the job for the whole darn subdivision.”

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If you don’t want to do a lot of measuring, you can use your pitch calculation to get an estimated square footage of your roof:

  1. Once you have your roof’s pitch, divide the number by 12. (For example, if your roof’s pitch is 4 in 12, you would divide 4 by 12. This would yield 1/3.)
  2. Next, square your result. (If your number is 1/3, squared would yield 1/9.)
  3. After that, add 1 to your number. (1/9 + 1 = 10/9.)
  4. Next, figure out the square root of your new number. (The square root of 10/9 is 1.05.)
  5. Determine the square footage of one floor of your home. (For example, if you have a two-story home that’s 2,600 square feet, one floor would be 1,300 square feet.)
  6. Multiply this number by your most recent result to get the estimated square footage of your roof. (1,300 x 1.05 = 1,365 square feet.)

Roof Measurement Companies

Things You Will Need

  • Square footage of your house

  • Pitch of your roof

  • Calculator

  • Paper and Pen


This calculation will give a solid estimate for a single slope roof and a simple gable roof with a single pitch. For more complex roof lines with multiple pitch angles, it’s a little more complicated but the same steps can be followed; just break down the roof into separate sections with a different square footage for each different pitch angle.

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