Holds for any shape.
I didn't wish to push the point beyond that. But since you brung it up, yup, 8 times volume and weight is correct, given body ratios remaining the same and height doubled.
To casual observers, without your knowledge, the previous commenters described such as only twice as big (i.e., twice the height), whereas you describe it as eight times larger, not due to observation, but due to the fact that you know the math behind the increase in size.
Consider a 5 year old child (about 3' tall) standing next to their parent (6' tall). Does the parent appear 8 times bigger? Obviously not, to the casual observer. Most would probably say three to four times bigger.