CRE glossary
Rentable vs usable square feet (RSF / USF)
Usable square feet (USF) is the floor area the tenant can actually use, desks, offices, conference rooms. Rentable square feet (RSF) is USF plus the tenant's pro-rata share of common areas (lobbies, restrooms, mechanical rooms, corridors). Rent is quoted on RSF, so understanding the ratio between RSF and USF is critical to comparing buildings honestly.
The ratio of RSF to USF is called the load factor (or add-on factor, or core factor, same thing). A typical Class A office building has a load factor of 12–18%, meaning a tenant with 10,000 USF will have 11,200–11,800 RSF and pay rent on the higher number. Inefficient buildings (older, oddly shaped) can run 25%+. Modern efficient towers run 8–12%.
Brokers compare buildings on $/USF when possible because that's the cost per dollar of useful space. A $80/SF Class A tower with a 18% load factor costs the same per usable foot as a $68/SF Class B with a no-load offering. Always ask the listing agent for both numbers; not knowing the load factor is how tenants accidentally pay 15% more for a 'cheaper' building.
BOMA (Building Owners and Managers Association) publishes the standard for measuring RSF and USF. Reputable landlords commission a BOMA measurement upon major renovation or every 5–10 years. Smaller / older buildings may have legacy measurements with significant errors, verify by asking for the BOMA report before LOI.
Load factor
Load factor = (RSF − USF) ÷ USF × 100%
Example
- Suite 1800 USF
- 10,420 SF
- Suite 1800 RSF
- 12,150 SF
- Load factor
- 16.6%
- Rent quoted at $58/SF on RSF
- $58 × 12,150 = $704,700/yr
- Effective rent on USF
- $67.63/USF
Broker perspective
When pitching a tenant on three buildings, normalize all rents to $/USF and present that side-by-side with $/RSF. The cheapest $/RSF is rarely the cheapest $/USF. The conversation becomes 'which building gives you the most usable space per dollar' instead of 'which has the lowest headline rate', and you'll pick a different winner half the time.
Frequently asked
People also ask
Do I pay rent on USF or RSF?
RSF. Always. The load factor is built into the comp record.
What's a normal load factor?
12–18% for Class A office. 8–12% for newer efficient towers. 18%+ for older / inefficient buildings. Above 20% is a red flag.
Can I negotiate the load factor?
No, it's a building-level number, not deal-level. But you can negotiate the base rent down to compensate for a high load factor.
How is RSF different from gross SF?
Gross SF is the entire floor area including walls, columns, and shafts. RSF excludes major shafts and elevators. USF excludes common areas. Always check which number you're being quoted.
Related terms
Base rent
The headline rent before pass-through expenses, usually quoted in $/SF/year and the starting point for every comp.
Load factor
The percentage of common-area square feet allocated to the tenant on top of usable space, typically 12–18% in Class A office.
Effective rent
Present-valued average rent over the term, net of free rent and TI, the real apples-to-apples cost number.
See rentable vs usable square feet (rsf / usf) extracted from a real lease.
Drop a 60-page lease, get a 38-field abstract in 90 seconds, every value cited back to the source page.