Calculate rentable vs usable area per the Building Owners and Managers Association (BOMA) 2017 Office Standard. Compute gross measured area, floor and building add-on factors, load factor, and building efficiency — essential for commercial leasing, real estate valuation, and Revit area planning.
This calculator implements the Building Owners and Managers Association (BOMA) 2017 Office Standard Method A to compute Gross Measured Area, Usable Area, Rentable Area, add-on factors, and load factor for commercial buildings. Engineers and real estate professionals use it during lease negotiations, building efficiency analysis, and Revit area plan validation.
BOMA Method A begins with the Gross Measured Area (GMA), which is the total floor area measured to the dominant portion of the exterior wall. Major Vertical Penetrations (MVPs) — elevator shafts, stairwells, and mechanical chases — are deducted to yield the Net Assignable Area. Floor Common areas such as lobbies, shared corridors, and multi-tenant restrooms are then subtracted to arrive at the Usable Area (UA) available to a single tenant.
The Floor Add-On Factor (F_AOF) equals Floor Common divided by Net Assignable Area. The Building Add-On Factor (B_AOF) equals total Building Common allocation divided by total building GMA. Rentable Area is then: RA = UA × (1 + F_AOF) × (1 + B_AOF). The Load Factor, expressed as a percentage, equals (RA − UA) / UA × 100, and represents how much common-area overhead a tenant absorbs beyond their usable space.
Building efficiency is the inverse metric: UA / RA × 100. A well-designed multi-tenant office building typically achieves 80–88% efficiency. Single-tenant buildings with minimal common area can approach 95%.
BOMA International publishes the ANSI/BOMA Z65.1-2017 Office Standard, which defines the measurement methodology used in this calculator. Method A (Dominant Portion) is the most widely adopted approach in the United States for commercial leasing and appraisal. The International Property Measurement Standards (IPMS) offer a globally harmonized alternative, but BOMA Method A remains the lease-document standard for U.S. office markets.
Revit area plans must be configured to match the BOMA boundary definitions: Floor area faces should align with the dominant portion rule, and Gross Building areas should exclude exterior wall thickness. The GSA (General Services Administration) uses a modified BOMA methodology for federal leases, requiring familiarity with both standards on government projects.
High load factors (above 18–20%) make a building competitively undesirable for tenants because they pay for common space at the same per-SF rate as usable space. Designers can reduce the load factor by minimizing dead-end corridors, clustering core elements, and narrowing exit stairwell widths to code minimums. Elevator lobbies that exceed code minimums inflate the load factor without adding tenant value.
Building shape matters: rectangular floor plates with a central core are more efficient than L-shaped or atrium configurations. Every additional restroom core placed off-center adds floor common area and raises the add-on factor. Mechanical rooms and electrical rooms placed within the rentable floor boundary (rather than on the roof or basement) also inflate GMA without increasing leasable revenue.
Enter your building name and type, then add one row per floor. For each floor, input the Gross Measured Area (measured from the exterior wall dominant portion), Floor Common area (lobbies, corridors, shared restrooms on that floor), the Building Common Allocation for that floor (each floor's prorated share of building-wide amenities), and Major Vertical Penetrations. The calculator automatically computes Usable, Rentable, Load Factor, and the overall Building Add-On Factor.
Review the Per-Floor Results table to identify floors with disproportionately high load factors — these are candidates for redesign. Compare Building Efficiency against the BOMA reference ranges on the right panel. Export the summary figures for inclusion in lease exhibits or pro forma spreadsheets.
Usable Area is the space exclusively controlled by a single tenant — their offices, private conference rooms, and private support areas. Rentable Area adds the tenant's proportionate share of floor common areas (corridors, shared restrooms) and building common areas (main lobby, fitness center) via the add-on factor. The tenant pays rent on the Rentable Area, not just the Usable Area.
Class A multi-tenant office buildings in major U.S. markets typically carry load factors between 12% and 18%. Buildings with generous lobbies, food service, or fitness centers can push to 20–22%. Single-tenant or build-to-suit buildings often carry load factors below 5% because building common areas are minimal.
BOMA 2017 introduced Method B (Interior Area) as an alternative that measures from the interior face of exterior walls rather than the dominant portion. Method B generally produces slightly smaller GMA figures and different add-on factors. Method A remains the dominant approach in U.S. lease negotiations, while Method B aligns more closely with international measurement standards.
In Revit, create an Area Plan with the BOMA area scheme. Place Area Boundary Lines at the dominant portion of exterior walls (typically the finished interior face of glass or the midpoint of masonry). Tag each area and assign it to the correct BOMA category (Usable, Floor Common, Building Common, or Major Vertical Penetration). Schedule the areas by category and compare totals against this calculator's outputs to validate your model.
Yes. Lower floors with larger lobbies, mail rooms, or retail typically carry higher load factors than upper office floors. This calculator computes a per-floor add-on factor based on each floor's common areas, plus a building-wide add-on factor applied uniformly across all floors. The combined load factor will therefore vary floor by floor, as shown in the Per-Floor Results table.
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