| Cubic millimeters per hour (mm³/hour) | Milliliters per hour (mL/h) |
|---|---|
| 1 Cubic millimeter per hour | 0.001 mL/h |
| 2 Cubic millimeters per hour | 0.002 mL/h |
| 3 Cubic millimeters per hour | 0.003 mL/h |
| 4 Cubic millimeters per hour | 0.004 mL/h |
| 5 Cubic millimeters per hour | 0.005 mL/h |
| 10 Cubic millimeters per hour | 0.01 mL/h |
| 20 Cubic millimeters per hour | 0.02 mL/h |
| 25 Cubic millimeters per hour | 0.025 mL/h |
| 50 Cubic millimeters per hour | 0.05 mL/h |
| 100 Cubic millimeters per hour | 0.1 mL/h |
| Reference | Cubic millimeters per hour (mm³/hour) | Milliliters per hour (mL/h) |
|---|---|---|
| A domestic shower | 540000000 mm³/hour | 540000 mL/h |
| A kitchen tap | 600000000 mm³/hour | 600000 mL/h |
| A garden hose | 900000000 mm³/hour | 900000 mL/h |
| The Amazon river | 7.524 × 1017 mm³/hour | 7.524 × 1014 mL/h |
The cubic millimetre per hour is a unit of volumetric flow rate equal to one cubic millimetre passing a point every hour. Its symbol is mm³/h. It is one of the smallest flow rates in ordinary use: a full hour delivers a volume the size of a grain of coarse salt, so it belongs to processes measured in days rather than minutes.
Corrosion is described in these terms whenever the loss is treated as a volume rather than a depth. A steel surface corroding at 0.1 millimetres a year loses, over a square centimetre, roughly one cubic millimetre a year — and the hourly rate that produces it is a ten-thousandth of that. Cathodic-protection engineers work with such numbers because the whole point of the discipline is to make a rate small enough to ignore for decades.
Permeation and leakage testing lives here too. A sealed package, a fuel line or a medical device is tested for how much fluid crosses its wall, and the answer is often a few cubic millimetres per hour or less. A leak too small to see over a working day becomes, at this rate, a measurable volume after a month in a heated test chamber.
Slow drug delivery uses the unit directly. An implanted osmotic pump may release a few cubic millimetres of solution per hour for weeks, and an intrathecal pump can be programmed in fractions of one. Because the reservoir holds only a few millilitres, the hourly rate determines how long the implant lasts before it must be refilled.
Botany borrows it for sap and exudates. Xylem flow in a single small vessel, latex from a tapped rubber tree between collections, and phloem exudate sampled from an aphid stylet are all of this order, and researchers report them per hour because the sampling period is measured in hours.
The scale is worth stating plainly. A litre is a million cubic millimetres, so a flow of one cubic millimetre per hour would take about a hundred and fourteen years to fill a one-litre bottle. That is why the unit almost never describes a bulk transfer — it describes a process one hopes will stay slow.
One cubic millimetre per hour equals 0.001 millilitres per hour, about 0.01667 cubic millimetres per minute, or one microlitre per 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.