Although it can vary depending on region, in most cases, after 161 characters another SMS will be added and charged.
Generally speaking, an SMS can be sent up to a maximum of 918 characters as a 6 part message, the maximum length of two-part, three-part, four-part, five-part and six-part concatenated text messages is 306 (2 x 153), 459 (3 x 153), 612 (4 x 153), 765 (5 x 153) and 918 (6 x 153) characters, respectively.