Lot Size Calculator

Calculate lot area in square feet and acres with buildable area after setbacks.

By Konstantin Iakovlev · Updated April 2026 · Source: HomeAdvisor

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Total Area

9,600 sqft

Acres

0.220

Buildable Area

4,500 sqft

Lot Details

Total Lot9,600 sqft
Buildable Area4,500 sqft
% Usable46.9%

Use the Lot Size Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.

How It Works

Knowing a parcel's total area in square feet and acres is only half the picture; what you can actually build on sits inside the setback lines. This tool reports both, isolating the buildable area that drives development potential. The stakes can be real — in a high-demand urban core, a 2026 residential project might gain 15% in property value for every additional 100 sq ft of buildable space.

Total area comes first, as Length x Width. From that the calculator subtracts the perimeter setback area — 2 * (Front Setback + Rear Setback) * Lot Width + 2 * (Side Setback + Side Setback) * Lot Length, adjusted for corner lots — to leave the buildable area. The initial pass treats the lot as a standard rectangle.

Setback rules shift from one jurisdiction and property type to the next, so local zoning ordinances are the final word. Uniform setbacks on every property line is a faulty assumption; corner lots routinely carry two 'front' setbacks instead of one. Easements deserve a look too, since they can trim the buildable area further than the setbacks alone.

Example: Calculating Buildable Area for a Residential Lot in Austin, TX (2026)

  1. 1 Input: A lot in Austin, TX, with a length of 120 feet and a width of 80 feet. Zoning requires a 25-foot front setback, a 10-foot rear setback, and 7-foot side setbacks. Let's assume a 2026 property value of $750,000 for the raw land.
  2. 2 Calculation: Total Area = 120 ft * 80 ft = 9,600 sq ft (0.22 acres). Buildable Length = 120 ft - (25 ft + 10 ft) = 85 ft. Buildable Width = 80 ft - (7 ft + 7 ft) = 66 ft.
  3. 3 Intermediate Result: Buildable Area = 85 ft * 66 ft = 5,610 sq ft.
  4. 4 Final Result: The total lot area is 9,600 sq ft (0.22 acres), with a buildable area of 5,610 sq ft. This 5,610 sq ft represents the maximum footprint for a structure, directly impacting the potential market value and development density, which for this Austin lot could represent $438,000 of its total value based on buildable area metrics.

Source: HomeAdvisor · Last updated: April 2026

Frequently Asked Questions

How do I calculate my lot size in acres?
Multiply the lot width by the lot depth in feet to get square footage. Divide by 43,560 to convert to acres. A 100 x 200 foot lot is 20,000 square feet or 0.46 acres. For irregular shapes, use a lot survey or county GIS mapping tool.
What is the average lot size for a house?
The median lot size for a new single-family home is about 8,000-9,000 square feet (about 1/5 acre). Urban lots average 5,000-7,000 square feet, suburban lots 8,000-15,000 square feet, and rural lots are often 1 acre or more.
How do setbacks affect buildable area?
Setbacks are the required distances from property lines where you cannot build. Typical setbacks are 20-30 feet front, 5-10 feet sides, and 15-25 feet rear. On a 60x120 lot with standard setbacks, your buildable area may be only 40-50% of the total lot.

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