| Liters per minute (L/min) | Cubic inches per minute (in³/min) |
|---|---|
| 1 Liter per minute | 61.0237440947 in³/min |
| 2 Liters per minute | 122.047488189 in³/min |
| 3 Liters per minute | 183.071232284 in³/min |
| 4 Liters per minute | 244.094976379 in³/min |
| 5 Liters per minute | 305.118720474 in³/min |
| 10 Liters per minute | 610.237440947 in³/min |
| 20 Liters per minute | 1220.47488189 in³/min |
| 25 Liters per minute | 1525.59360237 in³/min |
| 50 Liters per minute | 3051.18720474 in³/min |
| 100 Liters per minute | 6102.37440947 in³/min |
| Reference | Liters per minute (L/min) | Cubic inches per minute (in³/min) |
|---|---|---|
| A domestic shower | 9 L/min | 549.214 in³/min |
| A kitchen tap | 10 L/min | 610.237 in³/min |
| A garden hose | 15 L/min | 915.356 in³/min |
| The Amazon river | 1.254 × 1010 L/min | 7.65238 × 1011 in³/min |
The litre per minute is a unit of volumetric flow rate equal to one litre passing a point every minute. Its symbol is L/min. It is the unit of taps, showers and small pumps — the flows a person meets directly, at a rate slow enough that a minute is the natural interval to count over.
Household plumbing is specified in it almost everywhere. A modern shower head delivers 6 to 9 litres per minute, an older one 15 or more, a kitchen tap 5 to 10, and a bath filler 15 to 20. Water-efficiency regulations in many countries set maximum figures in exactly these terms, because the flow rate multiplied by a typical shower length gives the volume of water and the energy needed to heat it.
That calculation is the reason the unit matters beyond plumbing. Reducing a shower from 12 to 8 litres per minute cuts both the water and the heating energy by a third, and heating water is one of the largest energy uses in a house. A restrictor costing very little changes a household's energy bill measurably.
Medicine uses the unit for gases. Oxygen therapy is prescribed in litres per minute — 2 through a nasal cannula for mild supplementation, 15 through a mask with a reservoir in an emergency — and the flowmeter on the wall of a hospital room is calibrated in exactly this unit. Anaesthetic machines are set the same way.
Engines and compressors also appear here. A small air compressor delivers 100 to 200 litres per minute of free air; a car's cooling system circulates tens of litres per minute; a garden pump moves 20 to 60. In each case the number is the useful one because the equipment runs for minutes at a time rather than seconds.
Sixty litres per minute is one litre per second, so the two units differ by the same factor as the two time units. That makes the conversion easy to do mentally, and it explains why the same equipment is often described in litres per minute by its manufacturer and litres per second by the engineer designing the system it goes into.
One litre per minute equals about 0.01667 litres per second, 1,000 millilitres per minute, or about 0.22 imperial gallons per minute.
The cubic inch per minute is a unit of volumetric flow rate equal to one cubic inch passing a point every minute. Its symbol is in³/min. In the machine shop it is better known by its initials: MRR, the material removal rate, the single figure that says how fast a cutting process is turning solid metal into chips.
The calculation behind it is simple multiplication. Depth of cut times width of cut times feed rate gives the volume removed per minute, so a 0.2-inch depth at 1 inch wide with a feed of 30 inches per minute removes 6 cubic inches per minute. Every variable a machinist can change appears in that product, which is why it is the number used to compare one strategy against another.
Material decides what is achievable. Roughing aluminium on a rigid machine can exceed 100 cubic inches per minute, mild steel manages perhaps 10 to 20, stainless steel less, and nickel alloys used in turbine parts only a few. The limit is set by spindle power, by the rigidity of the setup and by the heat the tool can survive, in whichever order runs out first.
Spindle power connects directly to it. Each material has a specific cutting energy, roughly 1 horsepower per cubic inch per minute for steel and a third of that for aluminium, so a 20-horsepower spindle can sustain about 20 cubic inches per minute in steel. A quoted removal rate that exceeds the machine's power is arithmetic that the machine will settle in its own way.
Beyond cutting, the unit describes small imperial flows generally. Hydraulic pilot lines, lubrication systems, fuel injection test benches and adhesive dispensers on American equipment are all rated in cubic inches per minute, where the metric world would say millilitres per minute.
For scale, 61 cubic inches per minute is about a litre per minute, and 231 cubic inches per minute is exactly one US gallon per minute — the gallon being defined as 231 cubic inches. That exact relation is why hydraulic engineers move between the two units without a conversion table.
One cubic inch per minute equals about 16.39 cubic centimetres per minute, about 0.01667 cubic inches per second, or about 0.004329 US gallons per minute.