Cache Capacity = Number of lines $\times$ Bytes/Words per Line
Now what you are asking is Size of Cache tag directory,
Each Block/Line contains tag whether it is associative, direct or set-associative mapped cache.
Hence, Size of Cache tag directory = Tag Bits $\times$ Number of Lines(Blocks).
If the question mentions that there are some extra information(valid, modified or replacement bits) along with tag then,
Size of Cache tag directory = (Tag Bits + Valid bits + Modified bits + Replacement Bits) $\times$ Number of Lines.