| Liters per hour (L/hour) | Milliliters per minute (mL/min) |
|---|---|
| 1 Liter per hour | 16.6666666667 mL/min |
| 2 Liters per hour | 33.3333333333 mL/min |
| 3 Liters per hour | 50 mL/min |
| 4 Liters per hour | 66.6666666667 mL/min |
| 5 Liters per hour | 83.3333333333 mL/min |
| 10 Liters per hour | 166.666666667 mL/min |
| 20 Liters per hour | 333.333333333 mL/min |
| 25 Liters per hour | 416.666666667 mL/min |
| 50 Liters per hour | 833.333333333 mL/min |
| 100 Liters per hour | 1666.66666667 mL/min |
| Reference | Liters per hour (L/hour) | Milliliters per minute (mL/min) |
|---|---|---|
| A domestic shower | 540 L/hour | 9000 mL/min |
| A kitchen tap | 600 L/hour | 10000 mL/min |
| A garden hose | 900 L/hour | 15000 mL/min |
| The Amazon river | 7.524 × 1011 L/hour | 1.254 × 1013 mL/min |
The litre per hour is a unit of volumetric flow rate equal to one litre passing a point every hour. Its symbol is L/h. It is the unit of slow, sustained flows — the ones too gradual to watch, where what matters is how much has moved by the end of a working day rather than what the stream looks like now.
Irrigation is its clearest home. A drip emitter is rated at 2, 4 or 8 litres per hour, and an orchard is designed by counting emitters: two hundred trees with two 4-litre emitters each draw 1,600 litres per hour, so a three-hour watering delivers 4.8 cubic metres. Because the emitters run for hours, the hourly figure is the one that maps directly onto the water budget.
Fuel consumption is quoted the same way whenever an engine runs at a steady load rather than travelling. A generator burns 2 to 5 litres per hour, a farm tractor 10 to 20, a large marine diesel several thousand. Litres per hour is the honest unit for these machines because litres per 100 kilometres means nothing to something that does not move.
Heating appliances follow. An oil boiler is rated by its burner nozzle in litres per hour, typically 1.5 to 3 for a house, and the figure multiplied by the heating value of the oil gives the heat output in kilowatts. A hot-water tap that produces 8 litres per minute is 480 litres per hour, which is why the same equipment carries both numbers in different parts of its documentation.
Laboratory and process work uses the unit for pumps that must run all day. Peristaltic dosing pumps for chlorination, water treatment and fermentation feeds are specified in litres per hour, often with a turndown range like 0.5 to 20, because the point of such a pump is to keep a slow rate constant for weeks.
Leaks and losses are described here too. A dripping tap loses a few litres per hour, which is trivial in a minute and a hundred litres by the next morning. Water utilities express network losses this way for the same reason: a slow rate compounded over the hours of a year is what turns an unnoticed defect into a measurable volume.
One litre per hour equals about 0.000278 litres per second, 0.01667 litres per minute, or 0.001 cubic metres per hour.
The millilitre per minute is a unit of volumetric flow rate equal to one millilitre passing a point every minute. Its symbol is mL/min. It is the working unit of clinical medicine and of analytical chemistry, two fields in which the quantity delivered matters far more than the speed of delivery.
Intravenous infusion is the clearest case. A drip is set in millilitres per hour for slow fluids and in millilitres per minute for fast ones, and an infusion pump is programmed with a rate and a volume. A litre of saline given over four hours runs at about four millilitres per minute; the same litre given rapidly in an emergency may run at a hundred.
Liquid chromatography works in the same range. A conventional analytical column is run at one millilitre per minute, a figure so standard that it appears as a default in almost every published method. Narrower columns run proportionally slower, and the flow must be held steady to within a fraction of a per cent, because the time at which a compound emerges depends on it.
Anaesthetic and oxygen delivery use the unit too, though there the fluid is a gas. Oxygen therapy is prescribed in litres per minute, and the small adjustments within that are made in hundreds of millilitres per minute. In each case the rate is a prescription, and the equipment exists to hold it constant.
Sixty millilitres per minute is one millilitre per second, so the conversion between the two is the same factor as between minutes and seconds. That relationship makes it easy to move between the fast and slow ends of the same equipment: a pump specified in millilitres per minute can be reasoned about in millilitres per second by dividing by sixty.
For everyday scale, a millilitre per minute would fill a teaspoon in five minutes and a cup in four hours. It is a rate slow enough that watching it is uninformative, which is why the instruments that use it display a totalised volume as well as a rate.
One millilitre per minute equals about 0.01667 millilitres per second, 60 millilitres per hour, or 0.001 litres per minute.