Property Line Setback Calculator
Before you plan a build, addition, garage, or even a shed, check the property line setback requirements for your lot. Enter your lot size and the required front, rear, and side setbacks, and this calculator shows your buildable envelope — the rectangle of land you are actually allowed to build on.
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How to use this calculator
Start with your lot's width and depth in feet — these are usually on your plat map, deed, or the county assessor's website. Then enter the setback distances required by your local zoning code: front (street side), rear, and side (applied to both sides).
The calculator subtracts each setback from the lot to find the buildable envelope. If your zoning code only lists setbacks in the same units as your lot, enter them exactly as written; the defaults here are common examples, not your local rule.
How it works
The math is simple rectangle geometry. The buildable width is the lot width minus the side setback on both sides, and the buildable depth is the lot depth minus the front and rear setbacks:
Buildable width = lot width − 2 × side setback
Buildable depth = lot depth − front setback − rear setback
Buildable area = buildable width × buildable depth
Buildable share = buildable area ÷ (lot width × lot depth) × 100
For example, a 100 ft wide lot with 10 ft side setbacks leaves 80 ft of buildable width. The calculator assumes a rectangular lot; odd-shaped lots, easements, and height or coverage limits can reduce the real buildable area further. Setback rules vary by local zoning — the defaults are examples only, so verify your numbers with the local planning office before you build.
Frequently asked questions
What is a building setback?
A building setback is the minimum distance your structure must stay from a property line. Zoning codes set separate front, rear, and side setbacks, and the land between the property line and the setback line cannot have buildings on it. They protect light, air, privacy, fire separation, and access for utilities.
Where do I find the property line setback requirements for my lot?
Check your city or county zoning code, usually published on the planning department's website, and look for the setback table for your zoning district. If you are unsure which district you are in, call the local planning or building office with your address or parcel number. A licensed surveyor can also confirm where your property lines actually are.
What happens if I build inside a setback?
Building inside a setback can trigger a stop-work order, fines, and an order to remove or relocate the structure. In some cases you can apply for a variance before building, which lets the planning board grant an exception, but approval is not guaranteed. Always confirm setbacks before pouring foundations or buying materials.
Do corner lots have different setback rules?
Often, yes. Many zoning codes treat corner lots as having two front yards, so the larger front setback applies on both street-facing sides instead of the smaller side setback. This can noticeably shrink the buildable envelope, so confirm the corner-lot rule in your local code before sizing a project.
Do the default setbacks in this calculator apply to my property?
No. The defaults are common examples only and vary widely by city, county, zoning district, lot type, and structure. Enter the setback numbers from your own zoning code, and verify the results with your local planning office before making any building or buying decisions.