The API doesn't provide it.
Internally, the capacity is multiplied by a factor whenever add(..) is called while in full capacity. However, the Java specification doesn't say anything about this constant factor... Sun's implementation uses a factor of 1.5, so you have an upper bound of 1.5*size() for the capacity.
Remember that you can use trimToSize() to "compact" the list and make the capacity equal to size().
