| Cubic millimeters per minute (mm³/min) | Cubic feet per minute (ft³/min) |
|---|---|
| 1 Cubic millimeter per minute | 0.000000035314666724 ft³/min |
| 2 Cubic millimeters per minute | 0.000000070629333448 ft³/min |
| 3 Cubic millimeters per minute | 0.000000105944000172 ft³/min |
| 4 Cubic millimeters per minute | 0.000000141258666896 ft³/min |
| 5 Cubic millimeters per minute | 0.00000017657333362 ft³/min |
| 10 Cubic millimeters per minute | 0.00000035314666724 ft³/min |
| 20 Cubic millimeters per minute | 0.00000070629333448 ft³/min |
| 25 Cubic millimeters per minute | 0.0000008828666681 ft³/min |
| 50 Cubic millimeters per minute | 0.0000017657333362 ft³/min |
| 100 Cubic millimeters per minute | 0.0000035314666724 ft³/min |
| Reference | Cubic millimeters per minute (mm³/min) | Cubic feet per minute (ft³/min) |
|---|---|---|
| A domestic shower | 9000000 mm³/min | 0.317832 ft³/min |
| A kitchen tap | 10000000 mm³/min | 0.353147 ft³/min |
| A garden hose | 15000000 mm³/min | 0.52972 ft³/min |
| The Amazon river | 1.254 × 1016 mm³/min | 442845921 ft³/min |
The cubic millimetre per minute is a unit of volumetric flow rate equal to one cubic millimetre passing a point every minute. Its symbol is mm³/min. It measures flows so slight that a whole minute yields a volume the size of a coarse grain of salt, and it exists because a great deal of precision engineering happens at exactly that pace.
Electrical-discharge machining is the classic user. A wire eroder cutting hardened tool steel removes 20 to 100 cubic millimetres per minute, and a sinker eroder finishing a mould cavity may remove less than one. The rate is the whole economics of the process: a die that takes eight hours to cut cannot be quoted like one that takes eight minutes, and the removal rate is what separates them.
Grinding and honing are described the same way when the tolerance is tight. A creep-feed grinder roughing a turbine blade root runs at hundreds of cubic millimetres per minute per millimetre of wheel width, but a final spark-out pass approaches zero by design, because the last few micrometres must come off without heating the workpiece.
Adhesive and solder-paste dispensing lives here too. A dot of adhesive on a circuit board is a fraction of a cubic millimetre, and a dispensing valve laying a bead is programmed by rate so the bead stays the same width as the head speeds up and slows down around corners. Underfill, conformal coating and potting are all specified in this unit or its microlitre twin.
Biology and medicine borrow it for slow perfusion. Organ-on-a-chip devices, microdialysis probes and slow-release implants move fluid at single-digit cubic millimetres per minute, and cerebrospinal-fluid production in an adult is about 350 to 500 millilitres a day, which is roughly 250 to 350 cubic millimetres per minute — a useful reminder that the body itself works at this scale.
Sixty cubic millimetres per minute is one cubic millimetre per second, and a million is one litre. Put together, that means a flow of one cubic millimetre per minute would need almost two years to fill a one-litre bottle.
One cubic millimetre per minute equals 0.001 millilitres per minute, about 0.01667 cubic millimetres per second, or one microlitre 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.