Size

bit:    b  # a single 0/1 in a binary number
byte:   B  # a group of 8b
nibble:    #
word       #

kilobyte: KB  # 1024 bytes
megabyte: MB  # 1024 KB
gigabyte: GB  # 1024 MB

Radix

See radix for additional details.

computers use binary (base2)

bytes (8bits/0-255) are often expressed as a pair of hex numbers (4bits/0-15)