Setback, FAR and ground coverage, explained
Three numbers decide how big a house you can legally build on your plot: the setbacks, the ground coverage and the FAR. Everything else in a plan is design. These are arithmetic, and they come first.
Setback
Setback is the open strip you must leave between your building and each plot boundary — front, rear and both sides. What is left in the middle is your buildable envelope.
Setbacks grow with plot size, road width and building height, so there is no single national figure. As a rough guide for small residential plots: front 3–6 ft, rear 2–4 ft, sides 1.5–4 ft. Row-house plots with party walls may have no side setback at all. Your local authority publishes the exact table — use it, not this one.
Ground coverage
Ground coverage is the maximum percentage of your plot that the building footprint may occupy, typically 50–65% for residential plots. On a 1200 sq ft plot at 60% coverage you may build on 720 sq ft of ground — which is usually close to what the setbacks leave you anyway. Whichever is more restrictive wins.
FAR / FSI
Floor Area Ratio (also called FSI) caps your total built-up area across all floors as a multiple of the plot area. A FAR of 1.75 on a 1200 sq ft plot allows 2100 sq ft of total floor area — so about 700 sq ft on each of three floors, or 1050 on each of two.
FAR is the number that decides how many floors you can realistically build. Check it before you plan a G+2.
Working it out for your plot
| Step | Example: 30 × 40 plot |
|---|---|
| Plot area | 1200 sq ft |
| Setbacks: front 5, rear 3, sides 3 | Envelope 24 × 32 ft |
| Footprint from setbacks | 768 sq ft |
| Ground coverage limit at 60% | 720 sq ft — this is the binding one |
| FAR at 1.75 | 2100 sq ft total across floors |
| Practical answer | ~720 sq ft per floor, up to about G+2 |
Draw them, do not just calculate them
A buildable envelope on paper is an abstraction until you draw a bedroom inside it and find it is 11 ft wide instead of 12. Set the plot and setbacks in the editor and the envelope is drawn for you; every room you place afterwards is measured against it as you drag.
Check your local rules
Setback tables, coverage limits and FAR all vary by state, city, plot size and road width, and they change. Nothing on this page is a substitute for your local building bye-laws or for a licensed architect. Use it to understand the numbers, then get the real ones.
Frequently asked questions
What is setback in a house plan?
The open space you are required to leave between your building and each plot boundary. What remains inside those lines is the area you can build on.
What is FAR or FSI?
Floor Area Ratio (Floor Space Index) is the ratio of total built-up area across all floors to the plot area. A FAR of 1.5 on a 1000 sq ft plot allows 1500 sq ft of total construction.
How do I calculate buildable area?
Subtract the front and rear setbacks from the plot depth and the side setbacks from the width. Multiply the two. Then check that result against your ground coverage percentage and take whichever is smaller.