CMH means cubic metres per hour and CFM means cubic feet per minute. Both measure airflow: how much air a cooler or fan moves. To convert, multiply CMH by 0.589 to get CFM, or multiply CFM by 1.699 to get CMH. An 18,000 CMH cooler is about 10,600 CFM.
The units
- CMH (m³/h): cubic metres of air per hour. Used on most Indian and metric specifications.
- CFM: cubic feet of air per minute. Used in the US and by many HVAC consultants.
- m³/min: cubic metres per minute, common for HVLS fans. Multiply by 60 for CMH.
Conversion table
| CMH | CFM |
|---|---|
| 7,500 | 4,415 |
| 18,000 | 10,600 |
| 22,000 | 12,950 |
| 25,000 | 14,715 |
| 30,000 | 17,657 |
| 44,000 | 25,900 |
| 50,000 | 29,450 |
Use our CMH to CFM converter for any value.
Why airflow is the number to compare
For evaporative coolers and fans, airflow decides coverage. Tank size, body size and motor power matter, but two coolers with the same motor can move very different amounts of air. Always compare CMH or CFM first.
From airflow to area
Each model has a recommended coverage: about 1,000 sq ft for 18,000 CMH and 3,000 sq ft for 50,000 CMH in a normal-height shed. See how many coolers you need.
Air changes per hour
Another way to use airflow is air changes per hour (ACH): how many times an hour the air in the room is replaced.
ACH = airflow (m³/h) ÷ room volume (m³)
A 20 m × 15 m workshop with a 6 m roof holds 1,800 m³. One 18,000 CMH cooler changes its air 10 times an hour.
Watch out for
- Free-air figures: airflow drops once ducts, bends and grills are added
- Mixed units: check whether a quote is in CMH, CFM or m³/min before comparing
- Rounded numbers: small differences between brands are often rounding, not performance
Frequently asked questions
How do I convert CMH to CFM?
Multiply CMH by 0.589. For example, 18,000 CMH is about 10,600 CFM.
How do I convert CFM to CMH?
Multiply CFM by 1.699.
What does CMH mean in an air cooler?
Cubic metres per hour: the volume of air the cooler moves in one hour.
Is higher CMH better?
Higher CMH covers more area, but the right figure is the one matched to your floor and heat load.