| Cubic centimeters per minute (cm³/min) | Cubic feet per minute (ft³/min) |
|---|---|
| 1 Cubic centimeter per minute | 0.000035314666724 ft³/min |
| 2 Cubic centimeters per minute | 0.000070629333448 ft³/min |
| 3 Cubic centimeters per minute | 0.000105944000172 ft³/min |
| 4 Cubic centimeters per minute | 0.000141258666896 ft³/min |
| 5 Cubic centimeters per minute | 0.00017657333362 ft³/min |
| 10 Cubic centimeters per minute | 0.00035314666724 ft³/min |
| 20 Cubic centimeters per minute | 0.00070629333448 ft³/min |
| 25 Cubic centimeters per minute | 0.0008828666681 ft³/min |
| 50 Cubic centimeters per minute | 0.0017657333362 ft³/min |
| 100 Cubic centimeters per minute | 0.0035314666724 ft³/min |
| Reference | Cubic centimeters per minute (cm³/min) | Cubic feet per minute (ft³/min) |
|---|---|---|
| A domestic shower | 9000 cm³/min | 0.317832 ft³/min |
| A kitchen tap | 10000 cm³/min | 0.353147 ft³/min |
| A garden hose | 15000 cm³/min | 0.52972 ft³/min |
| The Amazon river | 1.254 × 1013 cm³/min | 442845921 ft³/min |
The cubic centimetre per minute is a unit of volumetric flow rate equal to one cubic centimetre passing a point every minute. Its symbol is cm³/min, and since a cubic centimetre is a millilitre, mL/min means the same thing. It is the standard unit of controlled gas flow in laboratories and in the semiconductor industry.
That industry gave it an abbreviation of its own: sccm, standard cubic centimetres per minute. The word standard matters, because a gas expands and contracts with temperature and pressure, so a volume flow means nothing until the conditions are pinned down. A mass flow controller set to 50 sccm delivers a fixed number of molecules per minute regardless of what the downstream pressure does, which is precisely what a deposition or etching process requires.
A silicon wafer passing through a plasma etcher meets several such controllers at once — argon at a few hundred sccm, a reactive fluorine compound at tens, oxygen at a handful — and the recipe that defines the process is essentially a list of these numbers against time. Repeating a process in another factory means reproducing the same flows.
Chromatography and gas analysis use the unit at the low end. Helium carrier gas through a capillary column runs at one or two cubic centimetres per minute, a flame detector burns hydrogen at thirty and air at three hundred, and a mass spectrometer's inlet is designed around a flow the vacuum pumps can cope with.
Liquids appear here as well, particularly in analytical chemistry and medicine. A high-performance liquid chromatography pump runs at 0.2 to 2 cubic centimetres per minute, and an intravenous infusion of 100 millilitres over an hour is 1.67 cubic centimetres per minute. In both cases the small, steady rate is what allows the result to be reproduced.
Sixty cubic centimetres per minute is one cubic centimetre per second, and a thousand is a litre per minute. So a typical mass flow controller set to 500 sccm is delivering half a litre of gas a minute — about the volume of a soft-drink bottle, which is a helpful way to picture what an invisible gas line is actually carrying.
One cubic centimetre per minute equals one millilitre per minute, about 0.01667 cubic centimetres per second, or 0.001 litres per minute.
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.