Cubic metre, but a litre or a cubic centimetre [= 1 millilitre] are much more widely used.
The customary unit of capacity for a bathtub is gallons.
Capacity isn't a unit at all. It's a characteristic, or a property of an item, which can be measured in whatever suitable unit. Capacity of batteries is measured in amp hours. Capacity of a gas tank can come in either liters or gallons.
Milliliters is the metric unit to use for the capacity of a thimble.
Capacity isn't a unit it is just a term that means how much a container holds. You can have metric units of capacity, such as Litres and Millilitres.
Metric
A millimeter is a unit of length, not a unit of volume or capacity. Perhaps you mean a cubic millimeter.
A litre is a unit of volume.
The unit is a litre.
There is no metric unit of capacity or volume that is equal to 1000 millimeters. This is because millimeters is length, and it has no relevance to capacity and/or volume.
decimeter is not related to capacity, it is in length.
(mAh) is the capacity. Click the link.
Litres