BTU / Tonnage / CFM Chart
The two conversions that tie cooling capacity to airflow: 1 ton = 12,000 BTU/hr (fixed) and 400 CFM per ton (rule of thumb, 350–450 range), tabulated from 1 to 5 tons. Use it to move between the tonnage on the nameplate, the BTU load, and the airflow the system should move.
Tons ↔ BTU ↔ CFM
| Tons | BTU/hr | Nominal CFM (400/ton) | CFM range (350–450) |
|---|---|---|---|
| 1 | 12,000 | 400 | 350–450 |
| 1.5 | 18,000 | 600 | 525–675 |
| 2 | 24,000 | 800 | 700–900 |
| 2.5 | 30,000 | 1,000 | 875–1,125 |
| 3 | 36,000 | 1,200 | 1,050–1,350 |
| 3.5 | 42,000 | 1,400 | 1,225–1,575 |
| 4 | 48,000 | 1,600 | 1,400–1,800 |
| 5 | 60,000 | 2,000 | 1,750–2,250 |
Fixed capacity, flexible airflow
The two numbers behave differently. The 12,000 BTU per ton is a definition, so the BTU column is exact for every tonnage. The 400 CFM per ton is a design target that you set within the 350–450 band based on the coil and the climate — lower airflow across a colder coil wrings out more moisture in a humid climate, higher airflow suits a dry climate or a heat pump. The one hard limit is the bottom: drop a DX coil below about 300 CFM/ton and it can freeze.
Get the tonnage itself from the cooling tonnage calculator or a load estimate, then use this chart to find the airflow — and the CFM calculator to work a specific space. For the load itself, the cooling load rules of thumb give a first-pass tonnage.
Common questions
How many BTU is a ton of cooling?
One ton of refrigeration equals 12,000 BTU per hour — the rate of heat removal needed to melt one short ton of ice in 24 hours. So a 3-ton system is 36,000 BTU/hr, and a 5-ton is 60,000 BTU/hr. It is a fixed definition, not a rule of thumb.
How many CFM per ton of cooling?
The comfort-cooling rule of thumb is 400 CFM per ton, with a normal design range of 350–450 CFM/ton. So a 3-ton system moves about 1,200 CFM. Unlike the BTU figure, this one is a rule of thumb — humid climates use lower airflow (colder coil, more dehumidification) and dry climates higher, but a DX coil should stay above about 300 CFM/ton to avoid freezing.
What is the difference between the BTU and CFM relationships?
12,000 BTU/ton is definitional and never changes. 400 CFM/ton is a design convention that depends on the coil and climate. That is why the table shows a single BTU value per ton but a CFM range — the airflow is a choice within the 350–450 band, while the capacity is fixed.
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