I assume you mean volume rather than capacity. The milliliter would be the best answer. It is 1 thousandth of a liter.
unit of capacity (a standardised measure by which volume can be expressed)
You have to know the conversion rate (like, 12 inches per foot or 100 centimeters per meter) and then just multiply the number you have in the larger measurement by the conversion rate: 2 feet * 12...
Capacity is volume, SI unit : cubic metre
milliliters