What is typically defined as the efficiency ratio for calculating gross square footage?

The efficiency ratio for calculating gross square footage represents the proportion of usable or assignable space within a building in relation to its total area. An efficiency ratio of 0.75 indicates that 75% of the total gross square footage is efficient space that can be utilized for its intended purpose, while the remaining 25% may consist of non-assignable areas such as hallways, walls, mechanical spaces, and other areas that do not directly contribute to the functional use of the building.

This value of 0.75 is commonly adopted in the industry, as it strikes a balance between maximizing usable space and accounting for necessary non-usable areas. A lower efficiency ratio might suggest a less efficient use of space, whereas a higher ratio (like 0.85) could be unrealistic in typical building scenarios, where some areas will always exist as circulation or support functions that do not directly contribute to usable square footage.

Overall, the 0.75 efficiency ratio provides a practical benchmark for architects and designers to evaluate their project planning and space utilization effectively.