Lot Size Calculator

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

By Konstantin Iakovlev · Updated September 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. Results are estimates from the numbers you enter and the assumptions described on this page; check them against local building codes, product specifications and current prices, and have structural, electrical or gas work designed or checked by a licensed professional.

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.

Total area comes first, as Length x Width, and dividing by 43,560 converts it to acres. The buildable area is the rectangle left after the setbacks: (Length − Front Setback − Rear Setback) × (Width − 2 × Side Setback), with the same side setback applied on both sides. The calculator treats the lot as a standard rectangle and makes no corner-lot adjustment.

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: Buildable Area for a 120 x 80 ft Lot

  1. 1 Input: A lot 120 feet long and 80 feet wide with a 25-foot front setback, a 10-foot rear setback and 7-foot side setbacks.
  2. 2 Total area: 120 × 80 = 9,600 sq ft; 9,600 ÷ 43,560 = 0.220 acres.
  3. 3 Buildable rectangle: (120 − 25 − 10) × (80 − 2 × 7) = 85 × 66 = 5,610 sq ft, or 58.4% of the lot.
  4. 4 Context: Easements and a second front setback on a corner lot can shrink the footprint further; the local zoning ordinance has the final word.

Source: HomeAdvisor · Last updated: September 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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