Understanding file sizes (Bytes, KB, MB, GB, TB)
A byte is a sequence of 8 bits. A single letter or character would use one byte of memory (8 bits), two characters would use two bytes (16 bits).
Put another way, a bit is either an 'on' or an 'off' which is processed by a computer processor, we represent 'on' as '1' and 'off' as '0'. 8 bits are known as a byte, and it is bytes which are used to pass our information in it's basic form - characters.
An alphanumeric character (e.g. a letter or number such as 'A', 'B' or '7') is stored as 1 byte. For example, to store the letter 'R' uses 1 byte, which is stored by the computer as 8 bits, '01010010'.
A document containing 100 characters would use 100 bytes (800 bits) - assuming the file didn't have any overhead (additional data about the file which forms part of the file).
Note, many non-alphanumeric characters such as symbols and foreign language characters use multiple bytes.