Rentable vs Usable Square Feet and the Load Factor
You pay rent on rentable area but you occupy usable area. The gap between them is the load factor, and it is negotiable more often than tenants realise.
Leasing · 542 words · updated 2026-08-26
Two suites can both be marketed as 10,000 square feet and give a tenant materially different amounts of space. The difference is measurement standard and load factor.
The three measures
- Usable area (USF) — what is inside the demised premises. The space you can put desks in.
- Rentable area (RSF) — usable area plus a pro-rata share of building common areas: lobbies, shared corridors, restrooms, mechanical and janitorial rooms on the floor and in the building core.
- Gross building area (GBA) — everything inside the exterior walls, used for construction and assessment purposes, not for leasing.
Load factor arithmetic
Load factor = (Rentable ÷ Usable) − 1
A 10,000 USF suite with a 15% load factor is quoted as 11,500 RSF. At $30.00 per rentable square foot the annual rent is $345,000 — an effective $34.50 per usable square foot. Compare offers on rent per usable foot, or on total annual dollars, never on the headline rate alone.
Typical loads: 8–12% for a full-floor tenant, 12–18% for a multi-tenant floor in a modern tower, and above 20% in older buildings with inefficient cores or in buildings that load amenity floors into the calculation. A full-floor tenant should push for a load close to the building's true core-and-shell factor, because it consumes no shared corridor.
Measurement standards matter
BOMA publishes the dominant office standards, and they have been revised repeatedly — 1996, 2010 (which introduced Method A "legacy" and Method B "single load factor"), and 2017. The 2017 standard permits inclusion of certain building amenity areas in the load, which can raise rentable area on the same physical suite without anything being built. Industrial and retail use different conventions again; retail is commonly measured to the centreline of demising walls and the exterior face of exterior walls.
Two questions belong in every LOI: which standard, which year, and who measured it? And: may we have the space re-measured by our own architect, with rent adjusted to the result? Landlords frequently agree to the second in a soft market.
Where tenants lose money
- Re-measurement mid-term. A lease that lets the landlord re-measure and restate rentable area on renewal, without a corresponding rent adjustment mechanism, is an open-ended cost.
- Amenity loading. A conference centre, fitness room or roof terrace loaded into the factor is effectively a mandatory add-on. Fine if you will use it; expensive if you will not.
- Expansion at a different load. Expansion space taken on a multi-tenant floor carries a higher load than the original full floor. Fix the expansion load factor in the original lease.
- Comparing to a different standard. Space marketed under BOMA 2017 will show more rentable feet than the same space under BOMA 1996. A "cheaper per foot" quote can be the more expensive deal.
Normalising a comparison
Build the comparison on total occupancy cost over the term, discounted:
- Take each offer's rentable area and rent schedule, including escalations.
- Add the operating expense load appropriate to that structure (see the NNN explainer).
- Subtract free rent and the tenant improvement allowance.
- Divide by usable square feet and by the number of years to get effective cost per usable foot per year.
That single number — net effective rent per usable square foot — is what should decide the deal.