CFM per Ton Converter
The standard rule of thumb in HVAC design is that 400 CFM of airflow provides approximately 1 ton (12,000 BTU/hr) of cooling capacity under normal conditions. This assumes a 20°F...
Formula
Source: ASHRAE Handbook | Last reviewed: June 7, 2026
Examples
400 CFM
= 1 ton
400 CFM ≈ 1 ton
1200 CFM
= 3 ton
3-ton system needs ≈ 1200 CFM
4000 CFM
= 10 ton
10-ton rooftop unit
Quick Reference Table
| CFM | Tons |
|---|---|
| 400 | 1 |
| 600 | 1.5 |
| 800 | 2 |
| 1200 | 3 |
| 2000 | 5 |
| 4000 | 10 |
Where is this used?
Used by engineers to quickly estimate the cooling capacity corresponding to a given airflow, or to determine required airflow for a specified tonnage.
Frequently Asked Questions
Is 400 CFM/ton always accurate?
No, it's a rule of thumb. Actual design values range from 350–450 CFM/ton depending on climate, humidity, and system design. High-humidity climates may use 350 CFM/ton for better dehumidification.
How does altitude affect this?
At higher altitudes, air is less dense, so more CFM is needed per ton. At 5000 ft, use approximately 480 CFM/ton as the rule of thumb.
What's the equivalent in metric units?
400 CFM/ton ≈ 54 L/s per kW ≈ 0.193 m³/s per kW. The same concept applies but in different units.
Reviewed for accuracy
· Last reviewed: June 7, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.