Able - if someone or something is able to do something, they have skills or qualities which make it possible for them to do it. Ex: She is an able teacher.( She is a teacher with quality ) Capable - if a person or thing is capable of doing something, they have the ability, capacity, or potential to do it. Ex:She is a capable teacher. ( She has the ability to be a teacher )

The primary difference is quantitative vs qualitative. Capacity is a measurable quantity. Ability/Capability are typically not measurable. "The capacity of the tank is 2000 liters". "The tank is able to hold 2000 liters." - this sounds awkward to me.. -- Ability vs. Capability is a bit hard to explain since people interchange them quite often. Ability is a quality that is "known". Capability is quality that is "possible". I am able to jump over this fence. - This implies that I know I can jump over the fence. I am capable of winning in poker. - This implies that it is possible Shooting a hole-in-one is beyond my capabilities - This implies that it is not possible for me to make that shot.. Capability can also be used to talk about limits w.r.t. capacity or for describing the features of a product. I am capable of buying this car. (As in.. I have the required financial capacity.. ) What are the capabilities of this armored tank?