Conversion from Cubic centimeters per second to US 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 US Gallon per minute (gal US/min)

The US gallon per minute is a unit of volumetric flow rate equal to one United States gallon passing a point every minute. Its symbol is gal US/min, and it is universally abbreviated GPM. It is the single most widely used flow unit in North America, appearing on pumps, wells, plumbing fixtures, irrigation designs and fire codes alike.

Plumbing fixtures are rated in it by federal standard. A showerhead in the United States is limited to 2.5 gallons per minute, a kitchen faucet to 2.2 and a lavatory faucet to 1.5, with stricter figures in some states. Because the flow rate multiplied by the minutes of use gives both the water and the energy to heat it, these limits do more for household energy than their modest numbers suggest.

Pumps are sold on curves drawn against this unit. A shallow-well jet pump delivers 5 to 15 gallons per minute, a submersible well pump 10 to 30, a swimming-pool pump 40 to 80, and a municipal pump thousands. Reading a curve at the required flow gives the head available and the horsepower drawn, which is how a pump is matched to a system.

Irrigation design is built on it. A sprinkler head is rated in gallons per minute, a zone is the sum of its heads, and the zone must not exceed what the supply can deliver — which is itself a figure in gallons per minute measured at the point of connection. Splitting a system into zones is entirely an exercise in staying within that number.

Fire protection uses it as its principal unit. Hydrant flow tests, standpipe requirements, sprinkler design densities and pumper truck ratings are all stated in gallons per minute, from a 1.5-inch hose line at 100 to an engine's 1,500 or more, and the national fire codes are written throughout in these terms.

For scale, one US gallon per minute is about 3.79 litres per minute, and 4.4 gallons per minute is about a cubic metre per hour. The imperial gallon is about 20 per cent larger, so a British pump described as 10 gallons per minute delivers about 12 US gallons per minute — a distinction worth checking on any imported equipment.

One US gallon per minute equals about 3.785 litres per minute, about 0.2271 cubic metres per hour, or about 0.8327 imperial gallons per minute.