Building Coverage Ratio Calculator
Calculate the percentage of your lot covered by buildings and other covered structures. Compare against zoning coverage limits to understand your site's development potential.
Lot Information
Building Footprints
Other Covered Areas
Coverage Limit (Optional)
Enter a coverage limit (like 35%) to compare your design against. This is for reference only and is not looked up from zoning codes.
Calculate Building Coverage
Enter your lot area and building footprints to see how much of your lot is covered by buildings. Optionally compare against a coverage limit.
Lot Area
Enter sq ft
Building Footprints
Add buildings
Fill in the form and click "Calculate Coverage" to see results
Understanding Building Coverage Ratio
What Is Building Coverage Ratio?
Building Coverage Ratio (BCR), also known as lot coverage or building coverage, is a measure of how much of a lot is covered by buildings and sometimes other covered structures. It is expressed as a percentage of the total lot area.
- Formula: Building Coverage Ratio = (Total Building Footprint Area / Lot Area) x 100%
- Example: A 2,000 sq ft building footprint on a 10,000 sq ft lot = 20% coverage
- Purpose: Zoning codes use coverage limits to control density, ensure green space, manage stormwater runoff, and maintain neighborhood character
How Building Coverage Differs from FAR (Floor Area Ratio)
Building Coverage Ratio and Floor Area Ratio (FAR) are related but distinct concepts:
Building Coverage Ratio (BCR)
- Measures footprint area (ground floor only)
- Considers horizontal extent of buildings
- Controls lot "openness" and green space
- A 2-story and 10-story building with same footprint have same BCR
Floor Area Ratio (FAR)
- Measures total floor area across all stories
- Considers vertical extent (building height/stories)
- Controls overall density and bulk
- A 10-story building has much higher FAR than a 2-story with same footprint
Together, BCR and FAR shape how buildings can be designed. A low BCR with high FAR encourages taller, slimmer buildings with more open space. A high BCR with low FAR results in sprawling, low-rise development.
Why Cities Use Coverage Limits
Municipalities establish building coverage limits for several important reasons:
- Stormwater Management: Impervious surfaces (buildings, pavement) prevent rainwater from absorbing into the ground, increasing runoff and flooding risk
- Green Space Preservation: Coverage limits ensure some portion of each lot remains open for landscaping, trees, and natural areas
- Neighborhood Character: Prevents lots from being completely filled with structures, maintaining visual openness and setbacks
- Light and Air: Ensures adequate sunlight and ventilation reach neighboring properties
- Privacy: Creates separation between buildings on adjacent lots
Typical Items That May Count Toward Coverage
Different jurisdictions have varying definitions of what counts as "covered area." Common items that may be included:
Often Included
- Main house footprint
- Attached garages
- Detached garages and accessory buildings
- Covered porches and carports
- Attached decks with roofs
- Pool houses and cabanas
Sometimes Included (Varies)
- Roof overhangs beyond a certain depth
- Pergolas and arbors
- Open decks without roofs
- Swimming pools
- Driveways and patios (sometimes separate impervious limit)
- Underground structures
Important: Always check your local zoning code for the specific definition applicable to your property. This calculator lets you include or exclude items based on your local rules.
Typical Coverage Limits by Zone Type
Coverage limits vary significantly based on zoning district and location. Here are some general ranges (always verify with local codes):
| Zone Type | Typical BCR Range | Notes |
|---|---|---|
| Rural/Agricultural | 5-15% | Large lots, minimal coverage |
| Single-Family Suburban | 25-40% | Most common residential zones |
| Single-Family Urban | 35-50% | Smaller lots, higher density |
| Multi-Family Residential | 40-60% | Apartments, condos |
| Commercial | 50-80% | Retail, office buildings |
| Downtown/Mixed-Use | 70-100% | Urban cores may allow full coverage |
Limitations of Simple Coverage Calculators
This Calculator is for Planning Only
- It uses only the areas you enter and does not look up actual zoning rules
- Local definitions of "coverage" vary and may include or exclude items differently
- Some jurisdictions have separate limits for building coverage and total impervious coverage
- The tool cannot verify measurements or account for irregular lot shapes
- Variances, overlays, and special districts may modify base requirements
- This is not a substitute for professional advice from architects, surveyors, or planners
Tips for Using This Tool
- Know your lot area: Check your property survey or deed for accurate lot dimensions
- Measure footprints carefully: Use building plans or measure the ground-floor outline of each structure
- Check your local code: Find out what items count toward coverage in your jurisdiction
- Run multiple scenarios: Try different layouts to see how adding or removing structures affects coverage
- Consult professionals: For permit applications or design decisions, work with an architect or planner
Frequently Asked Questions
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