Illustrative arithmetic using assumed figures, not a calculation for a real parcel; the governing LEP, map, site area and gross-floor-area definition must be checked for the project.
Floor space ratio is calculated by dividing gross floor area by site area, but the arithmetic is the easy part. A reliable NSW calculation must first verify the mapped maximum ratio and apply the definitions and site-area rules in the current instrument to every input.
Direct answer
For an assumed 600 m² site with a mapped maximum FSR of 0.5:1, the illustrative maximum gross floor area is 300 m². If the correctly classified existing and proposed gross floor area totals 285 m², the indicative FSR is 0.475:1 and the illustrative difference to the assumed mapped maximum is 15 m².
Those figures are assumptions for this worked example. They are not a result for a real parcel and do not decide which floor areas count. To run the same arithmetic on your own figures, use the free NSW floor space ratio calculator, which shows its working and applies the gross floor area categories below.
The FSR formula is reliable only after its inputs are resolved
Read the mapped control, verify the relevant site area and classify gross floor area before checking the arithmetic.
- Read the control
Retrieve the mapped maximum ratio and current written provision.
- Verify site area
Confirm the applicable land and any special site-area calculation rule.
- Classify GFA
Apply the current gross-floor-area definition to existing and proposed spaces.
- Check the result
Expose the calculation and keep other planning and design tests separate.
Decision boundary
The formula is deterministic after its inputs are established. Selecting the correct site area and classifying spaces under the applicable gross floor area definition can require drawings, survey information and professional review.
Inspectable FSR calculation
A Plynth-authored worked example that exposes every assumed input and calculation rather than presenting a pass/fail badge.
| Calculation step | Assumed value | Operation | Result |
|---|---|---|---|
| Site area | 600 m² | Source input | 600 m² |
| Mapped maximum FSR | 0.5:1 | Source input | 0.5 |
| Indicative maximum GFA | — | 600 × 0.5 | 300 m² |
| Existing counted GFA | 180 m² | Drawing/classification input | 180 m² |
| Proposed additional counted GFA | 105 m² | Drawing/classification input | 105 m² |
| Total counted GFA | — | 180 + 105 | 285 m² |
| Indicative proposed FSR | — | 285 ÷ 600 | 0.475:1 |
| Illustrative difference to assumed maximum | — | 300 − 285 | 15 m² |
Formula and source checks
The common formula can be expressed as:
floor space ratio = gross floor area ÷ site area
Before using it, retrieve the mapped ratio and current written provision from the applicable LEP. In the standard framework, clause 4.4 connects the maximum ratio to the Floor Space Ratio Map, while clause 4.5 defines the ratio and contains the site-area calculation rules. The Dictionary contains the gross floor area definition. The Standard Instrument is adopted and modified by individual LEPs; the applicable LEP remains the site-specific source. The NSW Planning Portal Spatial Viewer provides access to relevant incorporated map datasets.
Inputs that need evidence
- Site area: confirm the applicable land and any special site-area rule.
- Gross floor area: classify each space against the current definition; labels on a drawing are not sufficient evidence by themselves.
- Existing development: use measured or verified drawings where accuracy matters.
- Proposal: retain a schedule showing included and excluded areas.
- Mapped ratio: record the layer, value, parcel intersection and checked date.
Exceptions and failure modes
- The site can have more than one mapped ratio.
- Site-area rules can differ for certain development or land arrangements.
- Gross floor area definitions contain inclusions, exclusions and measurement boundaries that must be applied to the actual design.
- Incentive provisions or another planning instrument may alter the relevant standard subject to conditions.
- Meeting a maximum FSR does not establish permissibility or compliance with height, setbacks, heritage, flood, design or other controls.
Next questions
Verify the Height of Buildings and zoning layers, then identify the design and assessment questions that remain after the FSR arithmetic is complete.