Units of Airflow
Converting amongst the three most common measures of air flow

The three most common measures for the flow of air used to cool power amplification devices in power amplifiers are Cubic Feet per Minute (CFM), cubic Meters per hour (M3 / hr), and liters per minute (l / min). This page shows how to convert amongst these measures, and presents six examples with which to check your math!


Calculations

Basic Units:

1 Foot = 12 inches; 1 ft3 = 12 · 12 · 12 = 1728 in3

1 Meter = 39.37 inches; 1 M3 = 39.37 · 39.37 · 39.37 = 61023.378 in3

1 US Gallon = 231 in3 = 3.787 liters; 1 liter = 231 / 3.787 = 61 in3

1 M3 = 61023.378 / 1728 = 35.314 ft3  or  1 M3 = 61023.378 / 61 = 1000 l
and
1 ft3 = 1728 / 61023.378 = 0.028317 M3  or  1 ft3 = 1728 / 61 = 28.328 l
and
1 liter = 61 / 61023.378 = 0.001 M3  or  1 liter = 61 / 1728 = 0.0353 ft3

Volume per unit of Time:

1 CFM = 0.028317 M3 · 60 = 1.699 M3 / hr  or  1 CFM = 28.328 l / min

1 M3 / hr = 35.314 ft3 / 60 = 0.58857 CFM  or  1 M3 / hr = 1000 / 60 = 16.667 l / min

1 l / min = 0.0353 CFM  or  1 l / min = 0.001 M3 · 60 = 0.06 M3 / hr

Examples
(Tables corrected, 6 December 2005)

Units CFM M3 / hr l / min
10 CFM 10 17 283.3
10 M3 / hr 17 10 0.6
10 l / min 0.35 0.6 10
Units CFM M3 / hr l / min
20 CFM 20 34 566.7
20 M3 / hr 34 20 1.2
20 l / min 0.7 1.2 20
Units CFM M3 / hr l / min
30 CFM 30 51 850
30 M3 / hr 51 30 1.8
30 l / min 1.05 1.8 30
Units CFM M3 / hr l / min
50 CFM 50 85 1416.5
50 M3 / hr 85 50 3
50 l / min 1.76 3 50
Units CFM M3 / hr l / min
100 CFM 100 170 2833
100 M3 / hr 170 100 6
100 l / min 3.5 6 100
Units CFM M3 / hr l / min
150 CFM 150 255 4250
150 M3 / hr 255 150 9
150 l / min 5.3 9 150


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