A kilolitre or megalitre if a large pond.
cups
The meter.
Pounds
It would be millimetres.
5ml
cups
Millilitres would be the most appropriate measure.
Gallons
Which measure is most reasonable for the amount of liquid a bowl will hold
Centimetre.
A megabyte.
20 liters
The meter.
Centimeters.
It would be feet
you would use gallons to measure the capacity of a bathtub
You can use cups to measure a small can of juice.