| Cubic centimeters per second (cm³/s) | Liters per second (L/s) |
|---|---|
| 1 Cubic centimeter per second | 0.001 L/s |
| 2 Cubic centimeters per second | 0.002 L/s |
| 3 Cubic centimeters per second | 0.003 L/s |
| 4 Cubic centimeters per second | 0.004 L/s |
| 5 Cubic centimeters per second | 0.005 L/s |
| 10 Cubic centimeters per second | 0.01 L/s |
| 20 Cubic centimeters per second | 0.02 L/s |
| 25 Cubic centimeters per second | 0.025 L/s |
| 50 Cubic centimeters per second | 0.05 L/s |
| 100 Cubic centimeters per second | 0.1 L/s |
| Reference | Cubic centimeters per second (cm³/s) | Liters per second (L/s) |
|---|---|---|
| A domestic shower | 150 cm³/s | 0.15 L/s |
| A kitchen tap | 166.667 cm³/s | 0.166667 L/s |
| A garden hose | 250 cm³/s | 0.25 L/s |
| The Amazon river | 2.09 × 1011 cm³/s | 209000000 L/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.
The litre per second is a unit of volumetric flow rate equal to one litre passing a point every second. Its symbol is L/s. It is the unit of pumps, drains and ventilation — the scale at which a flow is large enough to be a design problem but small enough to belong to a single building.
A litre per second is a substantial stream. A kitchen tap fully open delivers about a fifth of it, a bath fills at roughly a third, and a fire hose runs at ten to twenty times as much. In visual terms it is a jet about as thick as a thumb moving briskly, and it would fill a domestic bath in about two minutes.
Building services are specified in this unit throughout Europe. Ventilation rates are given as litres per second per person — around eight to ten in an office, more in a room where people cook or exercise — and a designer multiplies that figure by the number of occupants to size the fans and the ductwork. The same unit describes rainwater drainage, where a roof's area and the local rainfall intensity together determine the flow a downpipe must carry.
Pumps are rated the same way. A domestic circulating pump moves a fraction of a litre per second, a borehole pump a few, and a large sewage pump hundreds. Because the power a pump needs is the flow multiplied by the pressure it must overcome, this figure sits at the centre of every pump calculation.
For gases the unit describes compressors and blowers, though there the volume depends on pressure and temperature and so must be stated at defined conditions. A compressor rated at fifty litres per second of free air is measured with the air at atmospheric pressure, and the same machine moving compressed air is shifting a far smaller volume.
A litre per second is a thousandth of a cubic metre per second, which is why hydrologists and building engineers rarely use the same unit even when they are describing the same water. A river carrying a cubic metre per second is carrying a thousand litres per second, and both figures are correct.
One litre per second equals 1,000 millilitres per second, 60 litres per minute, or about 0.0353 cubic feet per second.