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How to estimate the cost of building a house by the square foot

Updated March 23, 2017

There are many ways to estimate the cost of building a home design. Though not necessarily the most accurate method, using the total square footage of the house and a rule of thumb dollar per square foot for the area and type of house is an easy way to get a rough idea of the potential cost.

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  1. Calculate square footage. Although it seems this would be very straightforward, a major factor that can skew a building cost estimate is the difference between finished square feet and constructed square feet, which includes areas such as basements or garages that don't receive the same degree of work and therefore cost less. Unfinished rooms, such as basements and garages aren't free to build, though, so excluding them from an estimate will produce an artificially low figure.

  2. Identify price per square foot by region and style. Most cost per square foot estimates are given by region and assume an average house. If your house is not average, say, for example, it's going to include luxurious interior or exterior finishes and high-quality materials, using the average cost per square foot in the region is going to produce inaccuracies. Consult the builder for the best square footage estimates based on your particular home plan.

  3. Multiply, and, if necessary, add. In the most simple, but least accurate, estimates, multiply the square footage by the cost per square foot. A more precise estimate can be obtained by using different cost per square foot estimates for finished and unfinished space and adding the total costs for these areas together.

  4. Anticipate overruns. A cost estimate is just that, an estimate. Don't surprised if unforeseen expenses unique to a project (such as, say, levelling the terrain) cause the actual total cost to be somewhat higher, even as much as 10 to 15 per cent. This, however, also doesn't mean the cost can't come in lower. Understand your estimate to represent an area into which the total cost is likely to fall. Don't agree to a plan that's too expensive, or routine overruns can jeopardise the financing.

  5. Tip

    When working with a builder or architect, it's possible to drastically change the cost per square foot of a house design by changing the styles of windows, materials and other features. Ask for several different estimates based on different configurations to get the most for your money. Building costs are always changing, so don't necessarily rely on an old estimate. The national average square foot cost for home building was £54.30 in 2005 but had dropped to £42.60 by 2007. In other years, the price could increase or decrease further.


    Though they are included in the steps above, most cost per square foot estimations do not account for unfinished areas or different quality levels of construction. When obtaining a cost estimate based on square footage be sure to determine how the particular estimate addresses these factors.

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Things You'll Need

  • House plan or design
  • Square footage
  • Cost per square foot

About the Author

Joseph Nicholson is an independent analyst whose publishing achievements include a cover feature for "Futures Magazine" and a recurring column in the monthly newsletter of a private mint. He received a Bachelor of Arts in English from the University of Florida and is currently attending law school in San Francisco.

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