Select Calculate Efficiency % to compare total floor area and net usable area, or Estimate Usable Area to apply a project-specific percentage. Choose units for each area, then select Calculate.
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Building Efficiency Ratio Formula
The building efficiency ratio compares net usable area to total floor area. It shows what percentage of a building or floor plate can actually be used by occupants, excluding space used for cores, walls, circulation, mechanical areas, and similar non-usable space.
- BER = building efficiency ratio, as a percentage
- NUA = net usable area
- TFA = total floor area
To estimate net usable area from a known efficiency ratio, the calculator rearranges the same relationship:
- NUA = estimated net usable area
- TFA = total floor area
- BER = building efficiency ratio percentage
The calculator has two functions:
- Calculate Efficiency %: enter total floor area and net usable area to find the building efficiency ratio.
- Estimate Usable Area: enter total floor area and an efficiency percentage to estimate the net usable area.
Building Efficiency Considerations by Property Type
Efficiency depends on the project and its area definitions. Use measured project data or a clearly stated planning assumption; the calculator does not provide validated property-type benchmarks.
| Building type | Ratio to use | Measurement consideration |
|---|---|---|
| Class A office | Use project measurements | Floor plates and core layout |
| Standard office | Use project measurements | Usable space, corridors, restrooms, and service areas |
| Retail | Use project measurements | Back-of-house, service, storage, and circulation space |
| Warehouse | Use project measurements | Open floor areas and internal partitions |
| Hospital or lab | Use project measurements | Mechanical, clinical, safety, and circulation space |
How to Interpret the Result
| Efficiency result | General interpretation |
|---|---|
| 85% to 100% | 0% to 15% of the total area lies outside net usable area |
| 78% to less than 85% | More than 15% and up to 22% lies outside net usable area |
| 70% to less than 78% | More than 22% and up to 30% lies outside net usable area |
| Below 70% | More than 30% lies outside net usable area; this alone does not establish building quality |
Examples
Example 1: Calculate building efficiency ratio
You have a building with a total floor area of 10,000 sq ft and a net usable area of 8,500 sq ft.
The building efficiency ratio is 85%. The remaining 15%, or 1,500 sq ft, is non-usable space.
Example 2: Estimate net usable area
You have a total floor area of 20,000 sq ft and assume an efficiency ratio of 80%.
The estimated net usable area is 16,000 sq ft. The remaining 4,000 sq ft is used by non-usable areas such as cores, corridors, walls, and services.
FAQ
What is a good building efficiency ratio?
A suitable ratio depends on the project’s function and measurement definitions. Compare like-for-like measurements against project requirements rather than applying a universal quality grade. Essential circulation, structure and services are not necessarily wasted space.
Can net usable area be greater than total floor area?
No. Net usable area must be less than or equal to total floor area. If net usable area is larger than total floor area, one of the measurements is wrong or the areas are being defined differently.
What is excluded from net usable area?
Net usable area usually excludes building cores, stairwells, elevator shafts, mechanical rooms, major circulation areas, structural walls, service areas, and other space that occupants cannot directly use. The exact definition can vary by measurement standard, so use consistent area definitions when comparing buildings.
