How to calculate the area & scale for building plans

Updated February 21, 2017

Whether you are designing a new house or designing a new deck, one of the first steps is to create a building plan. Building plans aren't drawn to size, they are drawn to scale, which means that you "shrink" the area down and make a scale model on paper. How much to scale down depends on how large the plan is, how detailed you want those plans and how big your paper is.

Measure the longest part of your building project, in feet. For example, the projected length of your house is 10 metres (30 feet).

Measure the longest part of your paper, in inches. For example, the length of your paper is 25 cm (10 inches).

Divide step 1 by step 2. 10 metres (30 feet) / 25 cm (10 inches) = 0.4 metre/cm (3 feet / inch) This means that every 1 cm (1 inch) of paper space represents 0.4 metre (3 feet) of "real" length.


If you have an unusually long building plan, you may want to consider purchasing a roll of paper, which you can cut to size for your plan, rather than having half of the paper space empty. Add a few metres of length around the edge of your building project if you want a border around the edge. Use your scale drawing to calculate area by converting to "real" measurements before multiplying length by width. For example, if on paper, an area is 13 by 13 cm (5 by 5 inches), then 13_0.4 = 5.2 metre (5_3 = 15 feet), so 5.2 by 5.2 metre= 27.04 square metres (15 feet by 15 feet = 225 square feet).

Things You'll Need

  • Sheet of paper
  • Tape measure
  • Pencil
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About the Author

Stephanie Ellen teaches mathematics and statistics at the university and college level. She coauthored a statistics textbook published by Houghton-Mifflin. She has been writing professionally since 2008. Ellen holds a Bachelor of Science in health science from State University New York, a master's degree in math education from Jacksonville University and a Master of Arts in creative writing from National University.