| Cubic feet per minute (ft³/min) | Cubic centimeters per hour (cm³/h) |
|---|---|
| 1 Cubic foot per minute | 1699010.7954 cm³/h |
| 2 Cubic feet per minute | 3398021.5908 cm³/h |
| 3 Cubic feet per minute | 5097032.3862 cm³/h |
| 4 Cubic feet per minute | 6796043.1816 cm³/h |
| 5 Cubic feet per minute | 8495053.977 cm³/h |
| 10 Cubic feet per minute | 16990107.954 cm³/h |
| 20 Cubic feet per minute | 33980215.908 cm³/h |
| 25 Cubic feet per minute | 42475269.885 cm³/h |
| 50 Cubic feet per minute | 84950539.77 cm³/h |
| 100 Cubic feet per minute | 169901079.54 cm³/h |
| Reference | Cubic feet per minute (ft³/min) | Cubic centimeters per hour (cm³/h) |
|---|---|---|
| A domestic shower | 0.317832 ft³/min | 540000 cm³/h |
| A kitchen tap | 0.353147 ft³/min | 600000 cm³/h |
| A garden hose | 0.52972 ft³/min | 900000 cm³/h |
| The Amazon river | 442845921 ft³/min | 7.524 × 1014 cm³/h |
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.
The cubic centimetre per hour is a unit of volumetric flow rate equal to one cubic centimetre passing a point every hour. Its symbol is cm³/h, and because a cubic centimetre is a millilitre, mL/h means the same rate. It describes flows slow enough that nothing appears to move, yet fast enough to matter over a shift or a night.
Hospital infusion is its most common setting. A syringe driver or volumetric pump is programmed in millilitres per hour: maintenance fluid at 80 to 120 for an adult, a sedative at 5, a neonatal feed at less than 1. The nurse setting the pump and the pharmacist calculating the dose both work in this unit, and the dose in milligrams per hour follows from it and the concentration of the bag.
Leak testing uses the unit as a pass-or-fail criterion. A hydraulic fitting, a fuel connector or a refrigeration joint is given an allowable leakage of so many cubic centimetres per hour, measured by collecting what escapes over a long period rather than by watching for a drip. Regulations on refrigerant loss and on vehicle fuel-system emissions are written this way.
Lubrication systems are rated here as well. A centralised oil-drip system on a machine tool delivers a few cubic centimetres per hour to each bearing, and an air-line oiler set correctly gives one drop every few minutes. Too much and the oil contaminates the workpiece; too little and the bearing fails, which is why the rate is specified rather than left to judgement.
Evaporation and drying processes are quantified in the same terms. A solvent evaporating from an open dish, water lost from a laboratory culture, or condensate produced by a small dehumidifier are all naturally described per hour, because the observation period is an hour or a day rather than a second.
The relation to bigger units keeps the scale clear. A thousand cubic centimetres per hour is a litre per hour, and a full day at one cubic centimetre per hour yields 24 cubic centimetres — about a tablespoon and a half. That is the honest measure of what a slow flow accomplishes while nobody is watching.
One cubic centimetre per hour equals one millilitre per hour, about 0.01667 cubic centimetres per minute, or 0.001 litres per hour.