The standard length of SMS is 160 characters in Latin symbols (ASCII). It also varies depending on the message type, especially if it is a Unicode message or if the message uses any special characters.

A message with up to 160 characters uses up to one SMS message. If the message is more than 160 characters, one message is used up for 153 characters as the remaining 7 characters are used to concatenate the message when it is delivered to the handset. So, a maximum of 160 characters is considered as one SMS, 2 messages are used for 161-306 characters (=153_2), and so on. You can send messages up to 918 characters and this long message will use up to six SMS credits (918 = 153_6).