The maximum length of your message can be 612 characters long, though it’s worth noting that this is the equivalent of four SMS and you’ll be charged for four messages.

If you want to be charged for just one message you need to send 160 characters or less.

It is worth being aware that some characters, such as the Euro symbol, are actually worth two characters, and that if you add a carriage return or line break this is a character too, full details of the GSM alphabet can be found on this page