4.2 GB disk, 8380800 sectors|blocks

BLOCKS * 512 bytes = size
8380800    * 512 = 4290969600 bytes

BLOCKS / 2 = size  (each block is 1024 or 1K)
8380800    /   2 = 4190400 Kbytes

Size / by 512 bytes = blocks
4290969600 / 512 = 8380800 blocks

Estimate
2048 * size in MB = approx blocks needed
2048 * 4200 = 8601600 blocks