Conversion from US Gallons per second to Cubic millimeters per second

Information about the US Gallon per second (gal US/s)

The US gallon per second is a unit of volumetric flow rate equal to one United States gallon passing a point every second. Its symbol is gal US/s. The US gallon is exactly 3.785411784 litres, descended from the English wine gallon of 231 cubic inches, so one US gallon per second is a little under four litres every second.

Fire protection in the United States works at this scale. A fire hydrant flows several gallons per second, a pumper truck delivers 20 or more, and a large sprinkler system's design demand runs to tens. Fire codes state these figures in gallons per minute, but hydraulic calculations of friction loss in the mains use the per-second value, and the two are the same number divided by sixty.

Municipal water and wastewater engineering also reaches it. A neighbourhood water main carries a few gallons per second at peak hour, a lift station handles tens, and a treatment plant's influent hundreds. American practice usually states plant capacity in million gallons per day, and one gallon per second is 0.0864 million gallons per day — a conversion any water engineer performs from memory.

Industrial cooling and process water are described here as well. Condenser cooling water, quench flows and washdown systems all reach gallons per second, and the pump power required follows from the flow multiplied by the head, so an increase in flow of ten per cent shows up directly on the electricity bill.

The difference from the imperial gallon deserves a clear statement. The US gallon is about 17 per cent smaller than the imperial one, so the same numerical rate is a materially different flow on either side of the Atlantic. Equipment documentation should say which gallon it means, and prudent engineers convert to litres before comparing anything.

For scale, one US gallon per second is about 3.79 litres per second, and 0.264 US gallons per second is one litre per second. A flow of ten US gallons per second is nearly 38 litres per second, enough to fill a domestic bath in three seconds and comparable to a small stream.

One US gallon per second equals about 3.785 litres per second, about 0.003785 cubic metres per second, or about 0.8327 imperial gallons per second.

Information about the Cubic millimeter per second (mm³/s)

The cubic millimetre per second is a unit of volumetric flow rate equal to one cubic millimetre passing a point every second. Its symbol is mm³/s. A cubic millimetre is the volume of a grain of coarse salt, so this unit describes flows small enough that a full second delivers something barely visible.

Additive manufacturing made it a working number. A fused-filament printer's extruder is limited by how fast it can melt plastic, and that limit is expressed as a volumetric rate: a standard hot end manages 8 to 12 cubic millimetres per second, a high-flow one 25 to 40. Slicing software converts it into a print speed by dividing by the cross-section of the extruded line, which is why the same printer runs faster with a thin layer than a thick one.

Inkjet printing works at a far smaller scale still. A single droplet is a few picolitres, and a print head firing thousands of droplets per second from hundreds of nozzles adds up to only a few cubic millimetres per second in total. The unit is convenient here because it sits between the droplet and the ink cartridge without needing scientific notation.

Machining uses it for the material-removal rate of fine work. Wire electrical-discharge machining removes 20 to 100 cubic millimetres per minute, which is under two per second, and micro-milling with a tool a fraction of a millimetre across is slower again. Since removal rate governs both time and tool wear, it is the number a process engineer optimises.

Medical and laboratory devices are specified here when the volumes are tiny. Microfluidic chips, capillary electrophoresis and some infusion applications move flows of this order, and a cubic millimetre per second is exactly one microlitre per second, which is why the same rate appears under two names in different catalogues.

The unit's relation to the litre is worth holding: a million cubic millimetres make a litre, so a thousand cubic millimetres per second is one litre per second. A flow of ten cubic millimetres per second, typical of a 3D printer, would take about twenty-eight hours to fill a one-litre bottle.

One cubic millimetre per second equals 0.001 millilitres per second, 0.06 millilitres per minute, or one microlitre per second.