We’ve recently launched a new knowledge base article that includes a table of the GSM Character Set – these are the characters that you can send in an SMS – it’s important to note that while most only use one character space, some in the Extended GSM Character Set use two spaces, here’s why:
A text message can contain no more than 140 bytes. The GSM Character Set is encoded using 7-bits (instead of the usual 8-bits that make a byte). This means there can only be 160 characters in a single text message.
This 7-bit limitation means only 128 standard characters can be encoded. The GSM standard gets round this by also having the Extended GSM character set. These are another 10 characters which are actually sent by sending two 7-bit characters, an escape (ESC) character followed by another character. This means that 160 ‘a’ symbols can fit in a single SMS, but only 80 ‘£‘ symbols.