| Milliliters per hour (mL/h) | Liters per hour (L/hour) |
|---|---|
| 1 Milliliter per hour | 0.001 L/hour |
| 2 Milliliters per hour | 0.002 L/hour |
| 3 Milliliters per hour | 0.003 L/hour |
| 4 Milliliters per hour | 0.004 L/hour |
| 5 Milliliters per hour | 0.005 L/hour |
| 10 Milliliters per hour | 0.01 L/hour |
| 20 Milliliters per hour | 0.02 L/hour |
| 25 Milliliters per hour | 0.025 L/hour |
| 50 Milliliters per hour | 0.05 L/hour |
| 100 Milliliters per hour | 0.1 L/hour |
| Reference | Milliliters per hour (mL/h) | Liters per hour (L/hour) |
|---|---|---|
| A domestic shower | 540000 mL/h | 540 L/hour |
| A kitchen tap | 600000 mL/h | 600 L/hour |
| A garden hose | 900000 mL/h | 900 L/hour |
| The Amazon river | 7.524 × 1014 mL/h | 7.524 × 1011 L/hour |
The millilitre per hour is a unit of volumetric flow rate equal to one millilitre passing a point every hour. Its symbol is mL/h. It is the unit of slow, sustained delivery, and above all of the infusion pumps that keep hospital patients supplied with fluid, nutrition and medication over many hours.
An intravenous line is almost always programmed in millilitres per hour. Maintenance fluid for an adult runs at 80 to 125, a slow drug infusion at 5 to 20, and a paediatric or neonatal line at 1 or 2. Those are the numbers a nurse enters, and the pump converts them into the mechanical rate of a screw driving a syringe plunger.
At the bottom of that range the precision required is remarkable. A syringe driver set to one millilitre per hour is advancing the plunger by a fraction of a millimetre per minute, and it must do so smoothly enough that the drug arrives at a steady concentration rather than in pulses. The engineering of these devices is largely about eliminating the stiction that would otherwise make the delivery uneven.
Insulin pumps work below this again, in tenths of a millilitre per hour, and deliver in tiny discrete pulses rather than continuously. Implanted pumps for pain medication may run at a fraction of a millilitre per day, which is a thousandth of a millilitre per hour, and are refilled at intervals of months.
Outside medicine the unit describes laboratory perfusion, slow chemical dosing, and the leakage rates that a seal is designed to stay below. A seal specified to leak less than a millilitre per hour is losing about a cupful a week, which for many purposes is entirely acceptable and for others is a failure.
For scale, a millilitre per hour would take a full day to fill a tablespoon and about a month to fill a small cup. It is slow enough that the total delivered over a shift is the meaningful quantity, and every pump displays that alongside the rate.
One millilitre per hour equals about 0.01667 millilitres per minute, 0.000278 millilitres per second, or 0.001 litres per hour.
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.