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FLOOR AREA RATIO CALCULATOR CALIFORNIA
California Floor Area Ratio (FAR) Calculator
Combine existing and proposed counted floor space, subtract demolished space and calculate FAR against parcel area. Verify local inclusions, exclusions and limits.
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BEFORE YOU START
Coverage and FAR calculation guide →Get a more useful result
FAR uses qualifying building floor area divided by verified lot area. First establish which floors count under your city or county rules.
- Check the jurisdiction's definition of counted floor area, including garages and ADUs.
- Enter existing counted floors, proposed new area and demolished/removed area.
- If known, enter the applicable maximum FAR in decimal format, such as 0.50.
Example: Example: a 6,000-square-foot lot with 2,200 square feet main area, 400 other and a 600-square-foot addition.
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HOW IT WORKS
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WHY THIS TOOL MATTERS
What Floor Area Ratio Measures
FAR compares qualifying building floor area against lot area. It is different from lot coverage, which generally measures a footprint on the ground. A multi-story building can have a higher FAR even when its footprint occupies a relatively small portion of the parcel. The legal definition of floor area is jurisdiction-specific.
Determine Which Floor Areas Count
Before using the calculator, verify the local definition of qualifying gross floor area. Depending on the city, basements, garages, stairways, attics, accessory structures, ADUs and parking spaces may be included, excluded or adjusted. The tool does not make those classifications automatically. Enter only the floor area you have determined counts.
Existing and Proposed Floor Space
Existing counted space in the main building and other counted areas are recorded separately. Proposed qualifying additions are included. Floor space demolished or removed from the final count is subtracted, but removal cannot exceed the existing total. If an addition replaces an old room, avoid counting the same area twice.
SOURCE & CONFIDENCE LAYER
Strong Tools Explain What Is Known, What Is Estimated, and What Still Needs Verification.
Verified sourceOfficial local or state resource when available
Preliminary resultCalculated or rules-based planning guidance
User suppliedFacts you entered about the property or project
Needs verificationProperty-specific issue the tool should not guess
DETAILED GUIDANCE
Use the Result Correctly Before You Commit Time or Money
FAR Formula With Example
The FAR formula is qualifying total floor area divided by lot area. A 6,000-square-foot lot with 3,000 square feet of qualifying floor area has an FAR of 0.50, or 50% expressed as a percent of lot area. This is a mathematical example, not a claim that 0.50 is allowed at a specific property.
Compare to the Local Maximum
If you know the legally applicable maximum FAR for the parcel, enter that decimal ratio, for example 0.50. The calculator then computes theoretical counted floor-area capacity remaining or the amount over the limit. Other restrictions such as setbacks, height, parking, open space, fire access and recorded easements can further limit a proposal.
FAR and Second-Story Additions
An upper-floor addition commonly increases total counted floor area even when it leaves the ground footprint unchanged. It is important to coordinate the floor-plan area schedule with the lot area on the site plan. Existing and proposed areas should reconcile with architectural dimensions and the reviewing city's zoning calculations.
ADUs, Garages and Special Housing Provisions
Do not assume all California ADUs, garages or basements are excluded. Treatment depends on the local law and the applicable state housing pathway. Some housing provisions can restrict how local development standards apply to qualifying ADUs. Review the correct project facts rather than using a blanket exclusion.
How to Use the Output
Treat the result as a preliminary numerical check, not zoning approval. Use approved plans or verified field dimensions, confirm parcel area and accepted floor-area definitions, and put an existing/proposed schedule on the permit set when required. The calculator does not replace agency or professional review.
FREQUENTLY ASKED QUESTIONS
California Floor Area Ratio (FAR) Calculator FAQs
These answers explain how to interpret the tool and when local or professional verification still matters.
How do I calculate FAR?
Divide total counted floor area by lot area. For example, 3,000 divided by 6,000 produces FAR 0.50.
Does an upper floor count?
Usually qualifying upper-story floor area contributes to FAR, subject to the local definition.
Is FAR the same as building coverage?
No. FAR measures counted floor area on relevant levels, while coverage generally measures counted footprints.
Do garages and ADUs count?
That varies by jurisdiction and the project pathway. Verify the applicable ordinance and exclusions.
What is remaining floor area capacity?
The entered FAR maximum times lot area, minus total counted floor area. This is theoretical capacity, not approval to build.
What format should I enter a FAR limit in?
Use a decimal ratio such as 0.50, not the number 50 for fifty percent.
Can the calculator approve my addition?
No. Zoning and permit decisions require review of the full project and local rules.