What Floor Area Ratio Means and Why It Matters
Floor area ratio (FAR) is a number that tells you how much building space you can have on a piece of land. It is the total square footage of all floors in a building divided by the total square footage of the land underneath it. A property with an FAR of 2.0, for example, can have 200,000 square feet of building space on a 100,000-square-foot lot.
Cities and counties use FAR limits to control how densely buildings can be built in different neighborhoods. Zoning codes set a maximum FAR for each area — residential neighborhoods often have lower limits (0.5 to 1.5), while downtown commercial districts allow higher ones (4.0 to 10.0 or more). Understanding your property's FAR tells you what size building you can legally construct, what you can add to an existing structure, or whether a development plan fits within local rules.
Key Takeaways
- Floor area ratio is calculated by dividing the total square footage of all building floors by the total square footage of the land lot.
- Your zoning code sets a maximum FAR for your property, which you can find through your city or county planning department's zoning map and ordinance.
- When measuring building area, count every enclosed floor — basements, ground floor, upper floors, and mezzanines — but exclude parking structures, mechanical rooms, and unfinished attics in most jurisdictions.
- If your property's current FAR is below the zoning limit, you may be able to add square footage; if it is already at or above the limit, expansion is restricted.
Finding Your Lot Size and Zoning FAR Limit
Before you can calculate FAR, you need two pieces of information: the exact square footage of your land and the maximum FAR your zoning allows. Start by finding your property's deed or a recent property tax assessment — both list the lot size in square feet or acres. If you have the acreage, multiply by 43,560 to convert to square feet (one acre = 43,560 square feet).
Next, look up your zoning code. Go to your city or county planning department's website and search for the zoning map — it shows which zone your address falls into. Then find the zoning ordinance or code document for that zone; it will state the maximum FAR allowed. If the website is unclear, call the planning department directly and give them your address; they can tell you the zone and the FAR limit in one call. Some jurisdictions also allow you to view this information through an online parcel viewer or GIS map.
Measuring Total Building Square Footage
The numerator in the FAR calculation is the total square footage of all enclosed floors in the building. Measure or add up the square footage of every level: basement, ground floor, second floor, third floor, and any mezzanines. Use the interior dimensions (wall to wall) for each floor, then add them together.
What counts and what does not varies slightly by jurisdiction, so check your local code. Most places include all enclosed, climate-controlled space. Parking garages, open-air decks, mechanical rooms, and unfinished attics typically do not count. Basements usually do count, even if they are partially below grade. If you are unsure whether a specific space counts, ask your planning department — they interpret the code for your area and can clarify before you do the math.
The FAR Calculation: Step by Step
Once you have the lot size and the total building square footage, the calculation is straightforward:
- Write down the total square footage of all building floors (all enclosed spaces that count under your zoning code).
- Write down the total square footage of the land lot.
- Divide the building square footage by the lot square footage.
- The result is your floor area ratio.
Example: A building has a ground floor of 20,000 square feet and a second floor of 20,000 square feet, for a total of 40,000 square feet. The lot is 50,000 square feet. FAR = 40,000 ÷ 50,000 = 0.8.
If your zoning allows an FAR of 1.5, you could legally add another 35,000 square feet of building space (1.5 × 50,000 = 75,000 total allowed, minus the 40,000 already built). If your zoning allows only 0.8, you are already at the limit and cannot expand the footprint or add floors without a variance or zoning change.
What Happens When You Are Below or At the FAR Limit
If your current FAR is below the zoning limit, you have room to build. You can add square footage by expanding the footprint (making the building wider or longer) or adding floors, as long as the total does not exceed the maximum FAR. Other zoning rules still explore — setbacks, height limits, parking requirements — but FAR alone does not block you.
If your current FAR is already at or above the limit, you cannot add enclosed square footage without getting a variance or a zoning change. A variance is a formal request to the zoning board to allow an exception to the code; it requires a hearing and proof of hardship. A zoning change is a request to the city council to rezone the property to allow a higher FAR, which is a longer process. Both are possible but not may provide. If neither is an option, you can renovate or improve the existing space without adding square footage.
Common Mistakes When Computing FAR
The most frequent error is including space that does not count. Parking garages, open decks, and mechanical penthouses are often excluded from FAR calculations, even though they are part of the building. Check your local code before counting them. Another mistake is using the exterior dimensions of the building instead of interior dimensions — always measure wall to wall inside the building.
A third mistake is forgetting to include all floors. Basements and mezzanines are straightforward to overlook, but they count toward FAR in most places. If you are renovating and adding a basement level, that new square footage adds to your FAR total. Finally, some people confuse FAR with lot coverage (the percentage of the lot that the building footprint takes up). They are different — FAR accounts for height and multiple floors, while lot coverage is just the ground-level footprint.
When to Consult a Professional
If your calculation shows you are close to the limit and you are planning a major addition, have a surveyor or architect verify the lot size and building square footage. Small measurement errors can affect whether a project is legal. If you need a variance or zoning change, hire a land-use attorney or planning consultant — they know the local process and can present your case to the zoning board or city council.
Your planning department can also review your calculation for free and tell you whether it is correct under local rules. They cannot tell you whether a variance will be granted, but they can confirm the math and the zoning limit. If you are buying a property and want to know its development potential, this is worth doing before you close.
Frequently Asked Questions
Does parking count toward floor area ratio?
Parking structures usually do not count toward FAR, even if they are enclosed. Some jurisdictions exclude parking entirely; others count it only if it is above or below grade and integrated into the main building. Check your local zoning code or ask your planning department, because the rule varies by location.
What if my lot is an irregular shape?
Use the total square footage of the lot as shown on the deed or property tax record — that is the official lot size. If you are unsure, a surveyor can measure it. The shape does not matter; only the total area matters for the FAR calculation.
Can I have a building with an FAR higher than the zoning limit?
Not legally, unless you have a variance or the property is zoned differently than you think. If an existing building exceeds the FAR limit, it is usually grandfathered in — allowed to stay because it was built before the current zoning code took effect. You cannot expand it further without a variance.
Does basement square footage count toward FAR?
Yes, in most jurisdictions basements count fully toward FAR. Some codes exclude basements that are more than half below grade, but the majority include all basement space. Confirm with your planning department if you are adding a basement.
What is the difference between FAR and lot coverage?
Lot coverage is the percentage of the lot that the building footprint occupies at ground level. FAR accounts for all floors stacked on top of that footprint. A building can have low lot coverage but high FAR if it is very tall, or high lot coverage but low FAR if it is only one story.