Unfortunately, there is no conversion factor that can be used to convert the number of tape blocks used on a tape to the corresponding number of MB, GB or bytes.
Determining what the blocksize is for a tape, when multiplied by the number of blocks, can produce a fair estimate for the number of bytes of tape storage used.
For tape, the processing occurs as View writes information to a buffer.
When the buffer is filled, it is then written to tape.
With that, several reports can be in 1 block.
So, the estimate of (blocksize x # of blocks) is the most that can be offered as a suggestion.