Plot Ratio Calculator
Enter the site area and gross floor area to calculate the plot ratio (GFA ÷ site area) and check it against an optional maximum allowed ratio. A core Hong Kong planning density indicator.
Input Data
Results
At a glance:Plot ratio = GFA ÷ site area, the multiple of floor area developable per unit of site, a key density control in Hong Kong planning. Each Outline Zoning Plan (OZP) states the maximum plot ratio for different zones (e.g. residential R, commercial C). Allowed GFA cap = site area × allowed plot ratio; if the actual GFA is below the cap it is compliant.
Formula
Plot ratio = GFA / site area
Allowed GFA cap = site area × max ratio
Compliant if GFA ≤ cap
$$PR = \frac{GFA}{A_s}$$$$GFA_{\max} = A_s \times PR_{\max}$$$$GFA \le GFA_{\max}$$How to Use
- Enter the site area (m²).
- Enter the gross floor area (m²).
- Optionally enter the maximum allowed plot ratio.
- The tool outputs the plot ratio, allowed cap and check.
Case Studies
Residential site
500 m² site, 1,500 m² GFA.
Plot ratio 3.0; with limit 5.0 the allowed is 2,500 m², compliant.
Commercial site
1,000 m² site, 9,000 m² GFA.
Plot ratio 9.0; if the limit is 12 it can still develop.
FAQ
What is the relation between plot ratio and storeys?
Plot ratio ÷ site coverage ≈ average number of storeys. E.g. plot ratio 3 with 0.6 coverage gives about 5 storeys.
Where do I find the limit?
It is set by the Outline Zoning Plan and its notes for the zone, applied alongside Buildings Department regulations.
Related Tools
References
Content review: Calculatorism Construction Team. Results are for reference only; please refer to the relevant authorities for the official figures.