CFM Per Ton & Square Feet Per Ton — The Airflow Rules
The two rules of thumb every estimator carries: airflow per ton of cooling (400 nominal, 350 humid, 450 dry) and floor area per ton by building type. Both are published conventions with real spread — this chart states the ranges the independent sources actually agree on, and the caveats that keep them from becoming sizing mistakes. One ton = 12,000 BTU/hr, by definition.
CFM per ton of cooling
| Condition | CFM / ton | What it does |
|---|---|---|
| Nominal (most climates) | 400 | The standard airflow assumption equipment literature is written around |
| Hot-humid climate | 350 | Lower airflow = colder coil = more moisture removal (more latent capacity) |
| Hot-dry climate | 450 | Higher airflow shifts capacity sensible where latent load is minimal |
| Working tolerance | 300–500 | The ±20% band designers treat as the sane range around nominal |
Square feet per ton by building type
| Building type | Sqft / ton | Note |
|---|---|---|
| Office | 190–400 | Perimeter zones land low, interior zones high |
| Retail / department store | 175–320 | — |
| School classroom | 210–280 | — |
| Restaurant dining | 100–250 | Kitchens run heavier still |
| Residential | 380–700 | The old "1 ton per 400 sqft" habit oversizes tight homes and undersizes hot climates |
| Data center / server room | 50–150 | Equipment load dominates — compute it, don't rule-of-thumb it |
Use the rules for checks, the calculations for sizing
CFM/ton and sqft/ton are sanity checks for estimates and quick takeoffs. Actual airflow comes from the OEM expanded performance data (Manual S), and actual capacity from a load calculation (Manual J or equivalent) — never from this chart. Convert between tons, BTU/hr, and airflow with the cooling tonnage calculator and CFM calculator, and run the load itself with the BTU load calculator. Once tonnage and airflow are set, duct sizes follow from the duct sizing chart.
Common questions
How many CFM per ton of cooling?
400 CFM per ton is the nominal convention equipment literature assumes. Hot-humid climates design lower — around 350 — because slower air over a colder coil wrings out more moisture; hot-dry climates run about 450 to maximize sensible capacity. The working band is 300–500; the exact number for a given system comes from the manufacturer's expanded performance tables.
How many square feet does one ton of AC cool?
It depends on the building far more than the rule admits: offices land anywhere in 190–400 sqft/ton, restaurants 100–250, residences 380–700, and data centers as low as 50–150. The old "400 square feet per ton" habit oversizes tight modern homes and undersizes hot-climate or high-occupancy spaces — treat every number on this page as an estimate check, not a sizing method.
Why does lower airflow remove more humidity?
At 350 CFM per ton the same coil runs colder and the air spends longer in contact with it, so more of the capacity goes to condensing moisture (latent) and less to lowering temperature (sensible). Push airflow to 450 and the split moves the other way. That trade is the entire reason the convention is climate-dependent.
Can I size an air conditioner from square feet per ton?
No — and every source that publishes these ranges says so. The ranges are for sanity-checking an estimate, pricing a budget, or spotting a load calc that's wildly off. Actual equipment selection needs a Manual J (or commercial equivalent) load calculation and Manual S equipment selection against OEM data.
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