| Cubic centimeters per minute (cm³/min) | Cubic feet per hour (ft³/h) |
|---|---|
| 1 Cubic centimeter per minute | 0.00211888000344 ft³/h |
| 2 Cubic centimeters per minute | 0.00423776000688 ft³/h |
| 3 Cubic centimeters per minute | 0.00635664001032 ft³/h |
| 4 Cubic centimeters per minute | 0.00847552001376 ft³/h |
| 5 Cubic centimeters per minute | 0.0105944000172 ft³/h |
| 10 Cubic centimeters per minute | 0.0211888000344 ft³/h |
| 20 Cubic centimeters per minute | 0.0423776000688 ft³/h |
| 25 Cubic centimeters per minute | 0.052972000086 ft³/h |
| 50 Cubic centimeters per minute | 0.105944000172 ft³/h |
| 100 Cubic centimeters per minute | 0.211888000344 ft³/h |
| Reference | Cubic centimeters per minute (cm³/min) | Cubic feet per hour (ft³/h) |
|---|---|---|
| A domestic shower | 9000 cm³/min | 19.0699 ft³/h |
| A kitchen tap | 10000 cm³/min | 21.1888 ft³/h |
| A garden hose | 15000 cm³/min | 31.7832 ft³/h |
| The Amazon river | 1.254 × 1013 cm³/min | 2.65708 × 1010 ft³/h |
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 hour is a unit of volumetric flow rate equal to one cubic foot passing a point every hour. Its symbol is ft³/h, and in the gas trades it is abbreviated CFH. It is the unit of fuel gas supply throughout North America, where every appliance and every pipe is sized by it.
Natural gas is billed and metered in cubic feet, so the hourly rate is what a gas fitter works with. A domestic furnace consumes 80 to 150 cubic feet per hour, a water heater 40, a cooking range 65, and a whole house at design conditions perhaps 250. A residential meter is rated at 250 CFH and the service pipe at rather more.
Pipe sizing tables are built entirely around this unit. Given a length of pipe, a diameter and an allowable pressure drop, the table returns a capacity in cubic feet per hour, and the fitter compares it against the sum of the appliance ratings on that branch. Undersize the pipe and the burners starve when everything runs at once; oversize it and the material cost rises for no benefit.
The unit converts easily into heat. Natural gas carries roughly 1,000 British thermal units per cubic foot, so a rate in cubic feet per hour is very nearly the same number in thousands of British thermal units per hour. An appliance rated 100,000 British thermal units per hour therefore burns about 100 cubic feet per hour, which is why the two figures appear together on every rating plate.
Propane behaves differently and is worth stating separately. It carries about 2,500 British thermal units per cubic foot, so the same appliance needs less than half the volumetric flow, and a pipe sized for natural gas is generously large for propane. Confusing the two is a classic and dangerous error in the trade.
Beyond fuel gas, the unit describes slow air and gas flows in imperial practice: purge lines, instrument air, small blowers and laboratory gas supplies. Sixty cubic feet per hour is one cubic foot per minute, and 35.31 cubic feet per hour is one cubic metre per hour.
One cubic foot per hour equals about 0.02832 cubic metres per hour, about 28.32 litres per hour, or about 0.01667 cubic feet per minute.