House Extension Cost Calculator


Planning a house extension? Understanding the potential cost of your project is crucial. Our House Extension Cost Calculator is a handy tool that allows you to quickly estimate the expenses associated with extending your home. In this article, we’ll explain how this calculator works, how to use it, provide a practical example, and answer some frequently asked questions related to house extension costs.


To estimate the cost of your house extension, we use a straightforward formula:

Estimated Cost = Length (in feet) × Width (in feet) × Cost per Square Foot ($)

This formula calculates the total cost by multiplying the dimensions (length and width) of your extension by the cost per square foot.

How to Use

Using our House Extension Cost Calculator is simple:

  1. Enter the length of the extension in feet.
  2. Enter the width of the extension in feet.
  3. Input the cost per square foot in dollars.
  4. Click the “Calculate” button.

The calculator will instantly provide you with an estimated cost for your house extension project.


Let’s say you plan to extend your house with a room that is 20 feet long and 15 feet wide, and the cost per square foot is $100. Using the calculator:

  • Length: 20 feet
  • Width: 15 feet
  • Cost per Square Foot: $100

Upon clicking “Calculate,” the estimated cost will be displayed as $30,000.


  1. What factors can affect the cost of a house extension?
    • Several factors can impact the cost, including location, materials, labor costs, and the complexity of the design.
  2. Is this calculator accurate for all regions?
    • While it provides a good estimate, local variations in costs may not be accounted for.
  3. Should I include interior finishes in the cost calculation?
    • Interior finishes like flooring and fixtures are not typically included in the basic cost estimate provided by this calculator.
  4. Can I use this calculator for commercial extensions?
    • This calculator is primarily designed for residential house extensions.
  5. Do I need permits for my house extension?
    • Check with your local authorities; permits may be required for house extensions.
  6. Are there any hidden costs in house extensions?
    • Hidden costs may include structural upgrades or unexpected issues uncovered during construction.
  7. What’s the average cost per square foot for extensions in my area?
    • Research local construction costs to get a more accurate cost per square foot.
  8. Can I save money on my extension project?
    • Cost savings can be achieved through careful planning and obtaining multiple quotes from contractors.
  9. Is financing available for house extensions?
    • Some financing options, such as home equity loans, may be available for extension projects.
  10. Should I consult a professional before using this calculator?
    • It’s advisable to consult with an architect or contractor for a more accurate estimate.


Our House Extension Cost Calculator is a valuable tool to help you estimate the expenses of your extension project. While it provides a rough estimate, remember that actual costs may vary based on various factors. Always consult with professionals and obtain multiple quotes before starting your house extension project to ensure a more accurate budget. Happy planning and building!

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