Gross Building Area (GBA): A Must-Know Metric for CRE

In commercial real estate, precision matters — especially when it comes to property measurements. One of the most essential metrics investors, developers, appraisers, and brokers need to understand is Gross Building Area, or GBA.

Whether you’re evaluating a new acquisition, comparing property types, or preparing a lease, knowing the gross building area definition and how it’s calculated can give you a clearer view of a property’s value and usability.

What Is Gross Building Area?

Gross Building Area (GBA) refers to the total square footage of a building, measured from the outside face of exterior walls. It includes all enclosed floors of a building — both above and below grade — regardless of use.

This means GBA accounts for areas like:

• Lobbies
• Hallways
• Mechanical rooms
• Storage areas
• Elevator shafts and stairwells

Unlike other metrics such as rentable or usable square footage, GBA provides the full footprint of a building’s structure, not just the tenant-occupied areas.

According to Law Insider, GBA is commonly used in zoning regulations, building code compliance, and valuation assessments, offering a consistent standard across many municipalities and appraisal reports.

GBA vs. Other Measurements

To fully grasp the importance of gross building area in commercial real estate, it helps to understand how it differs from related metrics:

GBA is especially critical when evaluating industrial, flex, or office buildings, where non-usable spaces (like mechanical rooms or corridors) still carry value in appraisals or investment analysis.

Gross Building Area Calculation

Calculating GBA is straightforward — but requires precision. Here’s how it typically works:

GBA = Total floor area measured from the exterior face of all perimeter walls

This includes:

• All floors (basements, mezzanines, upper stories)
• Enclosed balconies and rooftop mechanical structures
• Elevator shafts and stairwells

Exclusions may include:

• Unenclosed porches
• Parking lots or open-air parking decks
• Rooftop terraces

Let’s say you’re evaluating a three-story office building with identical floor plates of 10,000 square feet. If each floor is fully enclosed and counted toward the GBA, your calculation would be:

GBA = 10,000 SF x 3 floors = 30,000 SF

For buildings with unique layouts, calculating GBA may require architectural drawings, site surveys, or third-party verification.

Why GBA Matters in CRE

Understanding gross building area isn’t just about being thorough — it’s a key driver in valuation, pricing, and strategy. Here’s how it can influence decision-making:

• Appraisals: Lenders and appraisers use GBA to determine market value, especially in non-residential properties.
• Development Planning: GBA informs FAR (Floor Area Ratio) calculations and compliance with local zoning ordinances.
• Acquisition: Buyers use GBA to benchmark pricing per square foot across comparable assets.
• Leasing Strategy: GBA affects how rentable square footage is derived and can influence how building efficiency is perceived.

In other words, knowing the GBA gives you the full picture — not just the polished front end of a space.

Final Thoughts

Gross Building Area is more than just a technical figure. It’s a foundational metric that impacts how commercial real estate assets are measured, compared, and valued. Whether you’re a tenant looking at space options or an investor analyzing an acquisition, a clear understanding of GBA helps ensure you’re working with the right numbers.

Looking to evaluate or list a property?

IPG brings market expertise and analytical precision to every deal. Reach out to our team to discuss how we can help you assess value, strategy, and opportunities — with GBA and beyond.