https://en.wikipedia.org/wiki/SMS
Maximum length of an individual SMS text is usually 160 characters in North America (based on old GSM standards with 7-bit characters). Although it could be 140 characters (on an 8-bit character set) or 70 characters (on a 16-bit character set).
Longer SMS texts (called "concatenated", "segmented", "linked", "multipart", or "long SMS") requires a few bytes of overhead (User Data Header) which actually reduce the maximum per-message length. Typical maximum length limits of "long" SMS texts are usually 153 7-bit characters (or 134 8-bit characters, or 67 16-bit characters). In theory, up to 255 discrete SMS segments can be concatenated into one "long" SMS.
In practice, most North American phones (that I've seen) default to GSM-based 7-bit character encoding and will only permit a "long SMS" composed of up to a maximum of five discrete/linked SMS segments (which all adds up to a total of 765 characters and "5 messages"). Some SMS software has options which can change the encoding and limits, although I've never changed them because I didn't want to risk breaking compatibility with the SMS settings on the network or on other people's devices.
