There are many words which are commonly confused with each other and which may have similar, overlapping, or even opposite meanings. Three such words are: ability, capability and capacity.
Ability refers to a person’s physical or mental skill or power to achieve something, e.g. the ability to ride a bicycle.
Capability refers more generally to power or ability, e.g. she has the capability to play soccer professionally, or to the quality of being able to use or be used in a certain way, e.g. a jet with long-distance-flight capability.
Capacity refers especially to a vessel’s ability to hold or contain something, e.g. a high-capacity fuel tank. However, used figuratively, capacity refers to a person’s physical or mental power to learn, e.g. an astounding capacity for mathematics.