082 · REAL ESTATE & CONSTRUCTION
Calculate current building coverage and floor area ratio from site, building and gross floor area, then reverse-calculate possible areas from target ratios.
CURRENT
Use site area as the common denominator to calculate coverage and FAR.
building area ÷ site area × 100
gross floor area ÷ site area × 100TARGET
Apply the entered target ratios arithmetically to the site area to estimate possible areas.
Target calculations use the same site area as the current-ratio section. 200㎡
site area × target coverage ÷ 100
site area × target FAR ÷ 100REFERENCE · Possible areas are arithmetic references based only on the target ratios you enter. Legal limits, zoning, district plans, height, parking, sunlight rules and permit eligibility are not determined automatically.
HOW TO USE
Enter the site area in m². The same site area is used as the denominator for both current-ratio calculations and target reverse calculations.
Enter building area and gross floor area to calculate coverage = building area ÷ site area × 100 and FAR = gross floor area ÷ site area × 100.
Enter a target coverage ratio or target FAR to reverse-calculate possible building area or possible gross floor area on the same site.
For example, a 200 m² site with 120 m² building area gives 60% coverage, while 400 m² gross floor area gives 200% FAR.
On a 300 m² site, target coverage of 50% gives 150 m² possible building area, while target FAR of 180% gives 540 m² possible gross floor area.
Treat the result as arithmetic reference data. Check zoning, district plans, height, parking, sunlight and other rules separately before making a legal or design decision.
BUILDING RATIO GUIDE
A 200 m² site with 120 m² building area gives 120 ÷ 200 × 100 = 60%. It is useful for understanding how much of the site is occupied by the building footprint.
A 200 m² site with 400 m² gross floor area gives 400 ÷ 200 × 100 = 200%. Because floor areas across levels are accumulated, FAR does not need to match coverage.
300 × 0.5 = 150 m². This is an arithmetic reverse calculation from the target ratio, not a statutory maximum or guaranteed buildable area.
300 × 1.8 = 540 m². The value does not choose the number of floors or a floor-by-floor layout, so it should not be treated as a finished design.
Current values come from entered areas, while target values are reverse-calculated from hypothetical ratios. Reading them side by side helps keep actual inputs separate from scenarios.
Statutory coverage and FAR can depend on zoning and exceptions, bonuses, or local rules. This tool is a calculator, not a regulatory database, so official sources remain the priority.
IMPORTANT NOTES
FAQ
Divide building area by site area and multiply by 100. A 200 m² site with 120 m² building area gives 60% coverage.
Divide gross floor area by site area and multiply by 100. A 200 m² site with 400 m² gross floor area gives 200% FAR.
No. Building area generally concerns the footprint on the site, while gross floor area combines floor areas across levels. Legal calculation rules can include additional details.
300 × 50 ÷ 100 gives 150 m² as the arithmetic possible building area.