Architectural Drawings & Design · Question

What does floor area ratio mean for how much I can build on my plot?

Short answer

Floor area ratio, also called floor space index, is the relationship between the total floor area of a building on all floors and the area of its plot. A higher permitted ratio lets you build more floor space on the same land, whether low and wide or tall and narrow. The local planning authority sets the value for your plot and use.

In more detail

Think of it as a floor space allowance. If the ratio allowed is one, you could build floor area equal to the plot area, in one wide floor or split into several narrower floors. The permitted ratio changes with the zone, the road width in front, the type of use and local rules, so a neighbour's plot may be treated differently from yours.

The ratio is only one of several controls. Setbacks from boundaries, height limits, ground coverage, parking requirements and open space also shape what is possible. A plot may therefore be unable to use its full ratio if another rule bites first.

What counts toward the total is also a local matter. Some areas such as stairs, lifts, parking and certain service spaces may be counted or excluded depending on the rules in force. Do not assume; ask your architect to confirm with the current regulations.

Same land, different shapes

Two owners with similar plots and the same allowance might build very differently. One chooses a wide single-storey factory with loading bays, the other a smaller footprint with a mezzanine and office floor. Both stay within the same floor space allowance, but they suit different operations and costs.

Before buying a plot or briefing a designer, ask for the permissible ratio, setbacks and height control from the competent authority or a professional who works with it. Beneficial or premium additional space may be available in some places, subject to approval and charges.

Key points

Floor area ratio links total built floor area on all levels to the plot area.
The local authority decides the permitted ratio for your plot, zone and use.
Setbacks, height, coverage and parking can limit use of the full ratio.
What counts toward floor area differs by place, so confirm with the current rules.
Check the ratio before buying land or finalising the building brief.

Who this applies to

Plot buyers estimating how much space they can build for business use.
Promoters planning a factory, warehouse or commercial building.
Owners considering vertical additions to an existing building.

Last reviewed 3 October 2026

This answer is general information, not advice on your particular case. Terms, eligibility, and requirements change, so check the current position with the relevant institution or authority.