When a commercial lease quotes rent at $35 per square foot, the square footage it's referring to isn't always the space the tenant actually occupies. It's the net rentable area, which includes not just the tenant's private space but also a proportionate share of the building's common areas.
Understanding that distinction is one of the most practical things a tenant, landlord, or investor can know before entering any commercial real estate transaction.
Net rentable area is the standard measurement used to calculate rent in commercial leases, value commercial properties, and compare buildings on a per-square-foot basis. It shows up in office leases, retail agreements, and industrial contracts, and the difference between what it includes and what the tenant actually uses can be significant enough to materially affect the economics of a deal on both sides.
This guide covers what net rentable area is, how it's calculated, and why it matters for tenants, landlords, and investors.
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What Is Net Rentable Area?
Net rentable area, is the total square footage on which a tenant's rent is calculated in a commercial lease. It includes the tenant's exclusively occupied space, called the usable area, plus a proportionate share of the building's common areas including lobbies, hallways, restrooms, stairwells, and mechanical rooms that serve all tenants collectively.
The formula is straightforward:
Net Rentable Area = Usable Area + Tenant's Pro Rata Share of Common Areas
The usable area is the space the tenant physically occupies and controls exclusively. The common area addition is calculated using a load factor, also called a loss factor or add-on factor, which represents the percentage of the building's common areas allocated to each tenant based on their share of the building's total usable area.
Net rentable area is the standard measurement basis for rent in commercial real estate because it distributes the cost of maintaining shared building infrastructure across all tenants proportionally.
A tenant occupying 10% of a building's usable area pays rent on 10% of the building's common areas in addition to their own space, reflecting their proportionate use of and benefit from those shared facilities.
Net rentable area is distinct from gross building area, which includes all space within the building's exterior walls including mechanical rooms, elevator shafts, and structural elements that are neither usable nor rentable. It is also distinct from gross leasable area, a term used primarily in retail real estate that is covered in section two.
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How to Calculate Net Rentable Area
The net rentable area calculation requires two inputs: the tenant's usable area and the building's load factor.
Usable Area is the space the tenant physically occupies, measured from the interior surface of the exterior walls to the centerline of shared walls with adjacent tenants. It includes private offices, workstations, conference rooms, storage areas, and any other space the tenant controls exclusively.
Load Factor is the ratio of the building's total rentable area to its total usable area, expressed as a percentage above 1.0. A load factor of 1.15 means that for every square foot of usable area, the tenant pays rent on 1.15 square feet of rentable area, with the additional 0.15 representing their share of common areas.
The Formula:
Net Rentable Area = Usable Area × Load Factor
Load Factor = Total Rentable Area ÷ Total Usable Area
Example of Net Rentable Area
A commercial office building has the following characteristics:
A tenant occupying 5,000 square feet of usable area in this building would have a net rentable area of:
5,000 × 1.15 = 5,750 sq ft
If the lease is priced at $40 per square foot annually, the tenant's annual rent obligation is:
5,750 × $40 = $230,000
Rather than the $200,000 they might have expected based on their 5,000 square feet of usable space alone. That $30,000 difference is the practical financial impact of the load factor, and it's why tenants should always ask for both the usable area and the rentable area before comparing lease options.
What Is Included and Excluded from Net Rentable Area
Included:
- Tenant's exclusively occupied office or commercial space
- Private restrooms within the tenant's suite
- Internal columns and structural elements within the tenant's space
- Pro rata share of building common areas including lobbies, corridors, shared restrooms, and mechanical rooms
Excluded:
- Elevator shafts and mechanical penthouses
- Exterior walls and structural elements outside the tenant's space
- Parking areas
- Space below grade that is not leased
BOMA Standards
The Building Owners and Managers Association publishes measurement standards that govern how rentable and usable areas are calculated in commercial real estate. The most widely used is the BOMA 2017 Office Standard, which provides precise definitions of what is included in usable and rentable area calculations and how common areas are allocated across tenants. Many commercial leases reference BOMA standards explicitly, and tenants who want to verify the accuracy of a landlord's net rentable area calculation should request that any measurement be conducted in accordance with the applicable BOMA standard.
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Net Rentable Area vs Gross Leasable Area: What's the Difference?
Net rentable area and gross leasable area are both measurements used to calculate rent in commercial real estate, but they apply to different property types and are calculated differently.
Net rentable area is the standard measurement for office and mixed-use commercial buildings. It includes the tenant's usable space plus a proportionate share of common areas, which means tenants pay rent on more square footage than they physically occupy.
Gross leasable area, commonly abbreviated as GLA, is the standard measurement for retail properties including shopping centers, strip malls, and retail parks. It measures the total floor area designed for tenant occupancy and exclusive use, including any areas used for receiving and storage of merchandise. Unlike net rentable area, GLA does not typically add a common area load factor on top of the tenant's occupied space. Common areas in retail centers including parking lots, food courts, and walkways are funded through common area maintenance charges rather than by inflating the rentable square footage.
Why the Distinction Matters
A tenant comparing an office lease quoted in net rentable area against a retail lease quoted in GLA is comparing two different things even when the per-square-foot rate looks similar. The office tenant is paying rent on space they don't physically occupy through the load factor. The retail tenant pays rent only on their occupied space but faces separate CAM charges for shared areas. Understanding which measurement basis applies to a specific lease is essential for accurately comparing the total occupancy cost of competing options.
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Conclusion on Net Rentable Area
Net rentable area is one of those commercial real estate concepts that looks straightforward until you realize the space you're paying rent on and the space you're actually using are two different numbers. The load factor is where that gap lives, and understanding it before you sign a lease or underwrite a property is the difference between accurate financial analysis and an expensive surprise.
For tenants, always ask for both the usable area and the rentable area, calculate the load factor, and compare total occupancy cost across competing spaces rather than per-square-foot rates alone. For investors and landlords, accurate net rentable area measurement is foundational to rent calculations, valuation, and NOI analysis. A measurement error that overstates or understates rentable area flows directly into every financial metric that depends on it.
