“How many tons per square foot?” is the first question on every commercial project — and the most dangerous one to answer with a single number. A 400-square-foot-per-ton rule that’s roughly fine for an office will undersize a restaurant by a factor of three and grossly oversize a warehouse. On commercial work, the building’s use drives the load far more than its floor area, so a square-foot rule is a sanity check, never a design.
This guide gives the planning figures by building type, explains why commercial loads behave so differently from homes, and shows the process that actually sizes the equipment. For the residential side, see AC Tonnage by Room Size.
Square Feet per Ton by Building Type
These are rough planning figures for cooling — useful for a first pass or a budget conversation, not for selecting equipment. Remember the counterintuitive part: a lower square-feet-per-ton number means a heavier load.
Square feet per ton by building type
| Building type | Approx. sq ft per ton |
|---|---|
| Server / data room | 50 – 100 |
| Restaurant | 100 – 150 |
| Retail | 250 – 350 |
| School / classroom | 250 – 300 |
| Office | 300 – 400 |
| Warehouse (conditioned) | 500 – 1,000 |
Look at the spread: a server room can need ten times the cooling per square foot of a warehouse. No residential rule of thumb comes close to capturing that, which is exactly why a generic “tons per square foot” answer is a trap on commercial work.
Why Commercial Loads Are Different
In a house, the cooling load mostly follows the building envelope — walls, windows, roof, and infiltration — with a handful of occupants. In a commercial building, internal gains usually dominate:
Why commercial loads are different
Three things swamp the envelope in most commercial spaces:
- Occupant density — a packed restaurant or classroom adds enormous sensible and latent load from people alone.
- Lighting, equipment, and process heat — kitchen line, server racks, retail displays, machinery. This is often the single largest component.
- Outdoor-air ventilation — code (ASHRAE 62.1) requires far more fresh air than a home, and conditioning that hot, humid outdoor air is a major load that scales with occupancy, not floor area.
How to Size a Commercial System Properly
The square-foot chart gets you to a budget number. Selecting equipment takes a real calculation:
Sizing a commercial system the right way
The key point for anyone coming from residential work: Manual J is residential only. The commercial equivalent is ACCA Manual N (with Manual Q for commercial duct design), which handles the occupancy schedules, ventilation rates, and internal-gain profiles that a home calculation never deals with. A commercial block load also has to account for the fact that the building’s zones — sunny perimeter, shaded core, kitchen, server closet — rarely peak at the same hour, which is why large buildings are zoned rather than served by one giant unit.
Special cases worth flagging
- Restaurants — kitchen hoods, cooking equipment, and dense seating make these among the heaviest loads per square foot, plus huge make-up air requirements.
- Server / data rooms — load is driven almost entirely by equipment kilowatts, not area. Size from the IT load (1 kW ≈ 3,412 BTU/hr), not a square-foot rule.
- Warehouses — often lightly loaded if minimally occupied, but high ceilings, dock doors, and any process equipment change the picture fast.
Worked example
A 5,000 sq ft general office at ~350 sq ft/ton pencils out to roughly 14 tons as a first-pass budget figure. But if half of it becomes a call center with dense seating and lots of equipment, the real Manual N load could push past 20 tons. The chart starts the conversation; the load calc ends it.
Estimate Commercial Tonnage
AC Tonnage per Square Foot Calculator — get a fast first-pass tonnage from area and use.
Use the AC Tonnage per Square Foot Calculator for a quick budget number, then commission a Manual N load calculation for anything you’re actually installing. To understand the load-calc fundamentals, see Heat Load & Cooling Load Calculation and Manual J vs Rule of Thumb — the same oversizing risks apply, with bigger dollars attached.
FAQ
How many tons of AC per square foot for commercial?
It depends heavily on use. Rough planning figures: offices 300–400 sq ft per ton, retail 250–350, schools 250–300, restaurants 100–150, conditioned warehouses 500–1,000, and server rooms 50–100. These are budget estimates only — commercial equipment should be sized from a Manual N load calculation.
Why can’t I use a single tons-per-square-foot rule for commercial?
Because commercial loads are driven by internal gains — occupancy, lighting, equipment, and ventilation air — that vary enormously by building use. A restaurant can need 3–5 times the cooling per square foot of an office, and a server room ten times a warehouse. A single rule will badly mis-size most buildings.
What is the commercial version of Manual J?
ACCA Manual N (Commercial Load Calculation) is the commercial counterpart to residential Manual J, paired with Manual Q for commercial duct design. Manual N accounts for occupancy schedules, ventilation rates, and internal and process gains that residential Manual J does not handle.
How do I size cooling for a server room?
Size from the equipment load, not floor area. Total the IT equipment power in kilowatts and convert at 1 kW ≈ 3,412 BTU/hr, then add lighting, any occupancy, and a safety margin for redundancy. Server rooms commonly land near 50–100 sq ft per ton, but the kilowatt load is the real driver.
Does ventilation affect commercial HVAC sizing?
Significantly. Commercial codes (ASHRAE 62.1) require much more outdoor air than homes, and conditioning that hot, humid ventilation air is a major part of the cooling load. It scales with occupancy rather than floor area, which is one more reason square-foot rules fall short on commercial work.