Volume and capacity
Volume is the space a solid takes up; capacity is how much a container holds.
A worked example
A tank 40 cm by 25 cm by 10 cm has volume 40 x 25 x 10 = 10 000 cm³. Since 1 000 cm³ is 1 L, it holds 10 L.
The mistake people actually make
Volume uses three dimensions, so the units are cubed. Doubling every edge multiplies volume by 8, not 2.