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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.
EveryCalc calculators are designed for fast, practical estimates with transparent inputs and no required account. We use plain formulas, visible assumptions, and related tools so visitors can check the result from more than one angle.
Results are informational only. For financial, tax, legal, medical, construction, or other high-impact decisions, verify the output against primary sources or a qualified professional.
Learn more about our review process on the EveryCalc methodology page.
How this calculator works
What this page estimates
This Common Area Factor Calculator is built to give a quick, browser-based estimate for common area factor. 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. The inputs stay on the page during normal use, and the result should be treated as an estimate for planning, comparison, or education rather than professional advice.
Calculation approach
The calculator applies the standard relationship implied by the inputs, then formats the answer so it can be checked and reused. For finance tools, the most important step is using consistent units, rates, time periods, and assumptions before comparing the result with another calculator or outside quote.
Example workflow
For example, start with a realistic value you already know, change one input at a time, and watch how the answer moves. That makes it easier to tell whether the result is being driven by the main amount, the rate, the time period, or a unit conversion.
Practical checks
- Use current, real-world numbers when the result affects money, health, tax, or legal decisions.
- Run a low, base, and high case when the inputs are estimates.
- Check the related calculators below when the next decision depends on a different assumption.
How to interpret the common area factor result
Best use
Use the result as a planning number for comparing payments, rates, returns, tax reserves, or cash-flow choices before you request a quote or make a commitment.
Cross-check
Compare the answer with the contract, lender estimate, tax form, brokerage statement, payroll record, or invoice that will control the real-world outcome.
Watch for
Do not rely on a single optimistic rate, return, or fee assumption. Money pages work best when you run low, base, and high cases and keep professional advice separate from the estimate.
This page belongs to the Finance calculator library, so the answer should be read in the context of the decision you are modeling rather than as a universal rule.
Before relying on this common area factor estimate
Most calculator mistakes come from the inputs, not the arithmetic. Use this short audit before you reuse the answer in a spreadsheet, quote, application, or important conversation.
Confirm source numbers
Match balances, rates, fees, taxes, income, and payment dates against the lender quote, payroll record, tax form, statement, invoice, or contract.
Separate cash flow from total cost
A lower monthly payment can still cost more over time if fees, interest, taxes, or a longer term are hidden in the structure.
Run conservative cases
Test at least one higher-cost or lower-return case before using the output for a purchase, refinance, investment, loan, or tax decision.
Rerun this page when the rate, price, term, fee, tax rule, income, expense, or expected holding period changes.
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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