Planning
Working prototype
Plot Ratio & GFA Calculator
From a site area and plot ratio to a buildable envelope in one screen.
The problem
At the very start of a project you need a rough sense of scale: how much can this site actually hold? The numbers are simple, but juggling plot ratio, site coverage, and floor efficiency in your head (or a spreadsheet you rebuild every time) slows down early massing.
What this does
Enter site area, plot ratio, site coverage, and floor efficiency. The tool returns your maximum GFA, an estimated storey count from the floor plate, the net usable area, and the residual open space — instantly, so you can feel the envelope before you draw it.
Try it
Loading tool…
What it does
Four inputs, one buildable envelope:
- Max GFA = site area × plot ratio.
- Floor plate = site area × site coverage.
- Estimated storeys = max GFA ÷ floor plate.
- Net usable area = max GFA × floor efficiency.
- Open space = whatever the footprint leaves behind.
Everything recomputes as you type, so you can dial the plot ratio up and down and watch the massing implications move.
Why it's useful
- Get a scale check in the first ten minutes of a project.
- Test the trade-off between coverage and height — a tighter footprint buys you storeys.
- Translate a planning parameter into something spatial you can reason about.
Honest limits
- Storeys are a first-pass estimate; they ignore setbacks, height limits, sky terraces, and non-GFA areas (car parks, plant, bay windows).
- Plot ratio definitions and GFA exemptions vary by authority — this is a napkin, not a submission.
- Always check the controlling URA Master Plan / authority guidelines for the actual controls on your plot.