Current research on sustainability of cities has favoured the implementation and conservation of greenery in the urban
context. The benefits of plants are not just environmental but recreational, aesthetic and emotional. The full benefits of plants
and the role they play in the ecology of cities remain to be mapped out but the general significance of plants appears to
be uncontested. This paper proposes a new architectural and planning metric for greenery in cities and buildings. This new
metric, the green plot ratio (GPR), is based on a common biological parameter called the leaf area index (LAI), which is
defined as the single-side leaf area per unit ground area. The green plot ratio is simply the average LAI of the greenery
on site and is presented as a ratio that is similar to the building plot ratio (BPR) currently in use in many cities to control
maximum allowable built-up floor area in a building development. GPR allows more precise regulation of greenery on site
without excluding a corresponding portion of the site from building development. It provides flexibility to the designer while
simultaneously protecting the green quota in the design. This concept has been applied in a number of design competitions in
which the author has collaborated with colleagues and various architectural practices. It has also been adopted as a planning
requirement by the client authority for one of the competitions for which the author has entered. While seen as a fundamental
and important metric, GPR is not in itself an indicator for all the ecological relationships between plants and cities. A larger
set of related metrics need to be developed.