Commercial Lease Square Footage Explained

Two different square footages

Every commercial lease involves two numbers, and confusing them is expensive.

Usable square footage (USF) is the space you actually occupy — your offices, your meeting rooms, your floor.

Rentable square footage (RSF) is your usable space plus your proportional share of the building’s common areas: lobby, corridors, restrooms, elevator banks, mechanical rooms.

You pay rent on the rentable figure. This is standard practice rather than a trick — those common areas are genuinely part of what makes the space usable — but it means the number in your lease is always larger than the number you could measure by pacing out your suite.

Load factor

The relationship between the two is the load factor, also called the common area factor or add-on factor:

Load factor = Rentable ÷ Usable

If you occupy 1,740 usable square feet and your rentable figure is 2,000, the load factor is 2,000 ÷ 1,740 = 1.15. You pay for 15% more space than you occupy.

Typical ranges:

Building type	Load factor
Single-tenant building	1.00 — no shared common area
Small multi-tenant office	1.10 – 1.15
Large Class A office tower	1.15 – 1.20
Buildings with extensive amenities	1.20+

A high load factor is not automatically bad — a building with a staffed lobby, good restrooms and wide corridors costs more to run and may be worth it. But it must be part of the comparison. Two suites both advertised as “2,000 sq ft” at the same rate are not the same deal if one has a 1.10 load factor and the other 1.20.

How rent is calculated

US commercial rent is normally quoted in dollars per square foot per year.

Annual rent = Rentable sq ft × Rate Monthly rent = Annual rent ÷ 12

For 2,000 RSF at $32/sq ft/yr:

• Annual: 2,000 × $32 = $64,000
• Monthly: $64,000 ÷ 12 = $5,333

The price per sqft calculator shows monthly and annual figures side by side, which makes comparing differently-quoted spaces much easier.

Watch for monthly quoting. Some markets, and most retail and industrial space, quote per square foot per month. A space at “$3.50 per square foot” is $42/sq ft/yr if monthly — very different from $3.50/sq ft/yr. Always confirm which basis is being used.

Lease types change the real cost

The quoted rate is not the whole cost. What it includes depends on the lease structure:

Full service gross (FSG) — the rate includes taxes, insurance, maintenance and usually utilities and cleaning. Simplest to budget for.

Modified gross — some costs included, others billed separately. Read carefully to see which.

Triple net (NNN) — the base rate excludes property taxes, insurance and common area maintenance, all billed on top. NNN charges commonly add $5 to $15 per square foot per year.

This matters enormously when comparing. A $22/sq ft NNN space with $9 in additional charges is $31/sq ft effective — more expensive than a $30/sq ft full service space that includes everything.

Always compare on effective rent, not the headline rate.

Other costs quoted per square foot

• Tenant improvement (TI) allowance — a contribution toward fitting out the space, quoted per rentable square foot. A $40/sq ft TI allowance on 2,000 RSF is $80,000.
• Common area maintenance (CAM) — your share of running the building, typically $3 to $12/sq ft/yr.
• Operating expense escalations — annual increases, often tied to an index or a fixed percentage.
• Parking — usually per space per month rather than per square foot, but sometimes bundled into the rate.

How much space do you need?

Space planning is also done per employee, and the conventional figures have shifted substantially:

Layout	Sq ft per employee
Traditional private offices	200 – 300
Standard mixed layout	150 – 200
Open plan	100 – 150
Dense open plan / hot desking	60 – 100

For 25 employees in a standard layout: 25 × 175 = about 4,375 usable square feet. At a 1.15 load factor that is roughly 5,030 rentable square feet, which is the number that will appear in the lease.

Add meeting rooms, a kitchen and storage on top if they are not already in your per-employee figure.

Questions worth asking

1. Is the quoted square footage rentable or usable?
2. What is the load factor?
3. Is the rate annual or monthly?
4. What lease type — gross, modified gross, or NNN?
5. If NNN, what are the current additional charges per square foot?
6. What is the annual escalation?
7. Is there a TI allowance, and is it per rentable or usable foot?
8. Which measurement standard was used — BOMA 2017 is the common one?

That last point matters more than it sounds. Different BOMA standards measure common areas differently, so the same physical suite can be quoted at different rentable figures depending on the standard applied.