Conversion from 3 Cubic centimeters per second to Gallons per minute

Information about the Cubic centimeter per second (cm³/s)

The cubic centimetre per second is a unit of volumetric flow rate equal to one cubic centimetre passing a point every second. Its symbol is cm³/s, and because a cubic centimetre is exactly a millilitre, the same rate is often written mL/s. It sits in the gap between the laboratory and the workshop: small enough to measure with a syringe, large enough to see.

Physiology uses it constantly. Resting cardiac output of five litres a minute is about 83 cubic centimetres per second, urine production is roughly 0.017, and a quiet breath moves perhaps 500 cubic centimetres over two seconds. Because the human body deals in volumes of this order, medical devices from ventilators to infusion pumps are calibrated in it.

Gas flow measurement adopted it early. A rotameter — the tapered glass tube with a float that appears on every laboratory bench — is graduated in cubic centimetres per second or per minute, and the float position gives the flow directly. Since a gas expands, such readings are meaningful only when the temperature and pressure are stated, which is why standard conditions accompany them.

Engines make an instructive example. A four-stroke engine of 2,000 cubic centimetres running at 3,000 revolutions per minute draws air through its intake at 1,500 cubic centimetres per revolution, or 75,000 cubic centimetres per second at 100 per cent volumetric efficiency. The mass air-flow sensor in the intake measures a quantity closely related to this, and the fuelling calculation depends on it.

Laboratory chromatography and analysis are specified here as well. A gas chromatograph column carries carrier gas at one to two cubic centimetres per minute, while a detector's make-up flow may be twenty or thirty, and the ratio between them determines the shape of the peaks the instrument reports.

The unit's convenience comes from the size of the cubic centimetre itself. A thousand of them make a litre, so a thousand cubic centimetres per second is a litre per second — a bath filling in about two minutes. Anything a person can pour by hand lies within a factor of a hundred of this rate.

One cubic centimetre per second equals one millilitre per second, 0.001 litres per second, or 60 cubic centimetres per minute.

Information about the Gallon per minute (gal/min)

The gallon per minute is a unit of volumetric flow rate equal to one imperial gallon passing a point every minute. Its symbol is gal/min, usually abbreviated GPM. The imperial gallon is 4.54609 litres, so this unit sits comfortably in the range of pumps, wells and building services, which is where it did most of its work before metrication.

Water wells and boreholes are still described by it in Britain and Ireland. A domestic borehole yields 2 to 10 gallons per minute, an agricultural one 20 to 60, and a public supply borehole several hundred. The yield test that establishes the figure runs the pump for hours while watching the water level, and the sustainable yield in gallons per minute is what determines whether a licence can be granted.

Pumps and pumping stations were rated in it throughout the industrial era. Boiler feed pumps, sewage pumps and fire pumps all carried plates in gallons per minute, and older British pump curves plot head against this unit rather than against cubic metres per hour. Anyone matching a replacement pump to an old installation has to convert the duty point carefully.

Building services used it for hot and cold water services, heating circuits and cooling towers. A heating circuit's flow follows from the heat it must carry and the temperature drop across the circuit, and in imperial terms the arithmetic came out in gallons per minute against a drop in degrees Fahrenheit — a combination that survives in many older plant rooms.

The unit also has a firefighting history. British fire brigade pumps were classified as light, medium and heavy by their output in gallons per minute, and hydrant flow tests, hose reel ratings and sprinkler system design all rested on the same figure before European standards moved the trade to litres per minute.

For scale, one gallon per minute is about 4.5 litres per minute, and 13.2 gallons per minute is one litre per second. A domestic shower running at 9 litres per minute is just under 2 gallons per minute, which puts everyday plumbing at the low end of the unit's range.

One gallon per minute equals about 4.546 litres per minute, about 0.2728 cubic metres per hour, or about 1.201 US gallons per minute.