CFM for 2.5-ton AC?
About 1,000 CFM using 400 CFM per ton.
This calculator converts cooling capacity into a residential supply-airflow target using the common 400 CFM per ton rule of thumb.
Choose tons mode or cooling BTU/hr mode. In BTU mode, tons = cooling BTU/hr ÷ 12,000, then CFM = tons × 400. The primary result is required airflow in CFM.
It does not design duct layouts, measure blower charts, or account for duct leakage. Use manufacturer blower data and Manual D for final duct design.
Concise answers for common searches — definitions, steps, and comparisons.
About 1,000 CFM using 400 CFM per ton.
12,000 BTU/hr of cooling capacity.
Airflow is estimated as cooling tons times 400 CFM per ton. BTU mode first converts cooling BTU/hr to tons by dividing by 12,000.
Formula
If tons mode: cfm = round(tons × 400). If BTU mode: tons = coolingBtu ÷ 12,000; cfm = round(tons × 400).Select tonnage mode or cooling BTU/hr mode depending on the capacity number you have.
Type AC tons (typical 0.5–10) or cooling BTU/hr. Example defaults: 2.5 tons or 30,000 BTU/hr.
Use the primary airflow result (tons × 400 CFM/ton) as a planning target for ducts or blower discussions.
Take the CFM into the Duct Size Calculator to estimate round duct diameter at a target velocity.
Input
Tons mode · 2.5Output
1,000 CFM2.5 × 400 = 1,000.
Input
BTU mode · 36,000 cooling BTU/hrOutput
1,200 CFM36,000 ÷ 12,000 = 3 tons; 3 × 400 = 1,200.
Common real-world scenarios where this tool saves time.
Enter 2.5 tons → about 1,000 CFM supply airflow target (2.5 × 400).
Enter 30,000 BTU/hr → 2.5 tons → about 1,000 CFM.
Enter 3.0 tons → about 1,200 CFM before checking duct diameter and static pressure with a pro.
Step-by-step chains that connect related tools for common tasks.
Convert tons or BTU to CFM, then estimate round duct diameter.
| Tons | Approx. CFM |
|---|---|
| 2.0 | 800 |
| 2.5 | 1,000 |
| 3.0 | 1,200 |
| 4.0 | 1,600 |
Use the installed or proposed cooling tons (or BTU) rather than guessing capacity from square footage alone.
After CFM, estimate round duct diameter and confirm with Manual D / a licensed HVAC technician.
Check the air handler or furnace blower chart for CFM at your static pressure—equipment may differ.
BTU mode expects cooling capacity (or cooling load). Heating BTU is not the input for this calculator.
This is a total airflow target. Supply and return design still need professional duct layout.
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This calculator uses 400 CFM per ton of cooling as a common residential rule of thumb. Actual equipment may specify a different CFM/ton.
Divide cooling BTU/hr by 12,000 to get tons, then multiply by 400. Example: 24,000 BTU → 2 tons → 800 CFM.
No. It is a planning default. High-static ducts, specialty coils, or manufacturer specs can require different airflow.
The result is a total system airflow target derived from cooling capacity. It does not split supply versus return paths.
Leakage reduces delivered airflow at the registers. This calculator does not add a leakage factor—seal and test ducts separately.
Prefer the equipment blower chart and Manual D design. Use this page only as a quick capacity-to-airflow estimate.
Duct CFM inputs remain local — EverydayTools does not collect duct-cfm calculator entries.
Estimates only — not professional HVAC or energy audit advice. Verify with a licensed contractor before purchasing equipment.
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Reviewed on 2026-06-28.
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1 ton = 12,000 BTU/hr