I am a little bit confused about how to calculate the memory capacity
This formula assumes that memory is word-addressable rather than byte-addressable. The number of words that can be addressed is $2^n$. If you want to convert this from words to bytes, you can use the formula (in which word stands for the word size in bits). If you want to convert it to kilobytes, for example, you need to multiply by the word size in bits, and divide by $8192$. And so on. Come up with your own formulas!