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Common Area Factor Calculator
Rentable SF is the billable number; usable SF is the actual tenant space. The common area factor (also called load factor) is the ratio. Tenants pay on rentable but only use the usable, and the difference is the building's common areas. This calculator converts between both and computes the effective rent per usable SF.
Common area factor (load factor)
1.143
Add-on factor
14.29%
Common area SF
1,500
Annual rent on RSF
$384,000
Effective rent / USF / year
$36.57
How the math works
Common area factor (CAF or load factor) = rentable SF ÷ usable SF. Tenants pay rent on rentable SF even though they only use the usable portion. A 1.14 CAF means 14% of the rent goes to shared spaces — lobbies, corridors, restrooms, mechanical.
Typical office CAF: 1.10-1.18. Larger floor plates tend toward 1.12-1.15. Small multi-tenant floors can hit 1.20+. Always confirm BOMA measurement standard — 1996 and 2017 differ.
How to Use
- Enter the rentable SF quoted by the landlord.
- Enter the usable SF measured inside the tenant's premises.
- Enter rent per rentable SF per year.
- Read CAF, effective rent per usable SF.
Frequently Asked Questions
BOMA vs historical measurement?
BOMA 2017 (IPMS-compliant) changed how common areas are counted. Many older leases still reference BOMA 1996 — can be a 2-4% difference in rentable SF. Always confirm which standard applies.
How to evaluate CAF?
1.10-1.15 is normal Class A office. 1.15-1.18 is acceptable on older buildings with more corridors/mechanical. Above 1.20 is aggressive — push back or negotiate lower rent per RSF to compensate.
Does CAF include parking?
No. Parking is typically a separate charge on a per-stall or per-SF basis. CAF only captures interior common areas within the leased floor/building.
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