The cubic foot per minute is a unit of volumetric flow rate equal to one cubic foot passing a point every minute. Its symbol is ft³/min, universally abbreviated CFM. It is the working unit of air movement in the English-speaking world: fans, compressors, extractors and air conditioners are all sold by it.
Ventilation is specified in it throughout North America. An extractor fan over a domestic cooker is rated at 200 to 400 CFM, a bathroom fan at 50 to 110, a large commercial rooftop unit at several thousand, and a whole-house fan at 3,000 or more. Building codes give minimum rates per person or per square foot of floor, and the designer multiplies to reach the fan size.
Compressed air uses it with a qualifier that matters. A compressor is rated in standard cubic feet per minute, referred to a fixed temperature, pressure and humidity, because a cubic foot of air at 100 pounds per square inch contains far more air than one at atmospheric pressure. A tool that consumes 5 SCFM will starve on a compressor rated 5 CFM of displacement, since displacement and delivery are not the same number.
Dust extraction in woodworking is a familiar case. A table saw needs about 350 CFM at the port to capture chips, a planer 400 to 800, and a shop with several machines running needs the sum plus an allowance for duct losses. Since a blast gate closes off unused branches, the same collector can serve the whole shop one machine at a time.
Engine and vehicle work uses it too. A carburettor is rated in CFM, an engine's airflow at peak power is quoted in CFM, and a radiator fan moves 1,500 to 3,000. The rating is what determines whether the airflow matches the engine's demand at the speed it is designed to work hardest.
The conversions are worth learning: 1 CFM is about 0.4719 litres per second, about 1.699 cubic metres per hour, and 2,119 CFM is one cubic metre per second. European and American catalogues describe the same equipment in these different units, and the numbers only match once one of them is converted.
One cubic foot per minute equals about 0.4719 litres per second, about 1.699 cubic metres per hour, or about 7.481 US gallons per minute.
| Unit | Symbol | 1 Cubic foot per minute equals | 1 of these equals | Converter |
|---|---|---|---|---|
| Milliliter per second | mL/s | 471.947443167 mL/s | 0.00211888000344 ft³/min | Cubic feet per minute to Milliliters per second |
| Milliliter per minute | mL/min | 28316.84659 mL/min | 0.000035314666724 ft³/min | Cubic feet per minute to Milliliters per minute |
| Milliliter per hour | mL/h | 1699010.7954 mL/h | 0.000000588577778733 ft³/min | Cubic feet per minute to Milliliters per hour |
| Liter per second | L/s | 0.471947443167 L/s | 2.11888000344 ft³/min | Cubic feet per minute to Liters per second |
| Liter per minute | L/min | 28.31684659 L/min | 0.035314666724 ft³/min | Cubic feet per minute to Liters per minute |
| Liter per hour | L/hour | 1699.0107954 L/hour | 0.000588577778733 ft³/min | Cubic feet per minute to Liters per hour |
| Cubic millimeter per second | mm³/s | 471947.443167 mm³/s | 0.00000211888000344 ft³/min | Cubic feet per minute to Cubic millimeters per second |
| Cubic millimeter per minute | mm³/min | 28316846.59 mm³/min | 0.000000035314666724 ft³/min | Cubic feet per minute to Cubic millimeters per minute |
| Cubic millimeter per hour | mm³/hour | 1699010795.4 mm³/hour | 5.88577778733 × 10-10 ft³/min | Cubic feet per minute to Cubic millimeters per hour |
| Cubic centimeter per second | cm³/s | 471.947443167 cm³/s | 0.00211888000344 ft³/min | Cubic feet per minute to Cubic centimeters per second |
| Cubic centimeter per minute | cm³/min | 28316.84659 cm³/min | 0.000035314666724 ft³/min | Cubic feet per minute to Cubic centimeters per minute |
| Cubic centimeter per hour | cm³/h | 1699010.7954 cm³/h | 0.000000588577778733 ft³/min | Cubic feet per minute to Cubic centimeters per hour |
| Cubic meter per second | m³/s | 0.000471947443167 m³/s | 2118.88000344 ft³/min | Cubic feet per minute to Cubic meters per second |
| Cubic meter per minute | m³/min | 0.02831684659 m³/min | 35.314666724 ft³/min | Cubic feet per minute to Cubic meters per minute |
| Cubic meter per hour | m³/h | 1.6990107954 m³/h | 0.588577778733 ft³/min | Cubic feet per minute to Cubic meters per hour |
| Cubic inch per second | in³/s | 28.799999998 in³/s | 0.0347222222247 ft³/min | Cubic feet per minute to Cubic inches per second |
| Cubic inch per minute | in³/min | 1727.99999988 in³/min | 0.000578703703745 ft³/min | Cubic feet per minute to Cubic inches per minute |
| Cubic inch per hour | in³/h | 103679.999993 in³/h | 0.00000964506172908 ft³/min | Cubic feet per minute to Cubic inches per hour |
| Cubic foot per second | ft³/s | 0.0166666666667 ft³/s | 60 ft³/min | Cubic feet per minute to Cubic feet per second |
| Cubic foot per hour | ft³/h | 60 ft³/h | 0.0166666666667 ft³/min | Cubic feet per minute to Cubic feet per hour |
| Fluid ounce per second | fl oz/s | 16.6102278896 fl oz/s | 0.0602038699677 ft³/min | Cubic feet per minute to Fluid ounces per second |
| Fluid ounce per minute | fl oz/min | 996.613673376 fl oz/min | 0.0010033978328 ft³/min | Cubic feet per minute to Fluid ounces per minute |
| Fluid ounce per hour | fl oz/h | 59796.8204026 fl oz/h | 0.0000167232972133 ft³/min | Cubic feet per minute to Fluid ounces per hour |
| Gallon per second | gal/s | 0.10381392431 gal/s | 9.63261919483 ft³/min | Cubic feet per minute to Gallons per second |
| Gallon per minute | gal/min | 6.2288354586 gal/min | 0.160543653247 ft³/min | Cubic feet per minute to Gallons per minute |
| Gallon per hour | gal/h | 373.730127516 gal/h | 0.00267572755412 ft³/min | Cubic feet per minute to Gallons per hour |
| US Gallon per second | gal US/s | 0.124675324667 gal US/s | 8.0208333339 ft³/min | Cubic feet per minute to US Gallons per second |
| US Gallon per minute | gal US/min | 7.48051947999 gal US/min | 0.133680555565 ft³/min | Cubic feet per minute to US Gallons per minute |
| US Gallon per hour | gal US/h | 448.831168799 gal US/h | 0.00222800925942 ft³/min | Cubic feet per minute to US Gallons per hour |