This floor area ratio calculator takes the figures you already have and applies the relationship behind floor area ratio calculations for you, giving floor area ratio (far) or floor space index (fsi), carpet to built-up area ratio and open space ratio (osr) from common area, open space area, indoor area, loading factor (lf), total land area, number of units and walls area.
What Is the Floor Area Ratio Calculator?
The floor area ratio calculator turns common area, open space area, indoor area, loading factor (lf), total land area, number of units and walls area into floor area ratio (far) or floor space index (fsi), carpet to built-up area ratio and open space ratio (osr), so you can order the right amount of material the first time.
Material estimates are where projects go over budget. Getting the quantities right before the delivery arrives is worth more than any discount on the order.
How to Measure for the Floor Area Ratio
Measure everything in the same unit and take the largest dimension you can reasonably use rather than the average. Formwork, ground conditions and cutting waste all push the real figure above the theoretical one.
Where a plan calls for a specific thickness, check it against local building regulations before you order. The calculator reflects the relationship, not the code.
Allowing for Waste and Errors
Order a little more than the calculation suggests. The gap between the theoretical quantity and what actually arrives on site is normally waste, spillage, over-excavation and uneven grading, and all of it comes out of the same budget.
Write the figures down and compare them with what you actually used on site. That is how you build an estimate you can trust for the next job.
A Worked Example
Working through an example, with common area set to 10, open space area set to 5, indoor area set to 2, the calculator returns carpet area of 0, and builtup area of 2, and total built up area of 10. Substitute your own figures and the same steps produce the same kind of answer.
Frequently Asked Questions
What do I need to work out floor area ratio (far) or floor space index (fsi)?
Enter common area, open space area, indoor area, loading factor (lf), total land area, number of units and walls area. The calculator then works through the relationship and reports floor area ratio (far) or floor space index (fsi), carpet to built-up area ratio and open space ratio (osr).
What does the floor area ratio actually calculate?
It takes common area, open space area, indoor area, loading factor (lf), total land area, number of units and walls area and converts them into floor area ratio (far) or floor space index (fsi), carpet to built-up area ratio and open space ratio (osr) using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter common area?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Do I have to fill in every field?
Only the fields a particular result depends on. If you leave one blank, the results that need it simply show a note instead of a number, and everything else still works.
Does anything you type get stored?
No. The whole calculation runs inside your browser, and nothing you enter is uploaded, logged or sent anywhere.