Text messages are sent in segments, which are the number of text messages it takes to send your text. A segment can have 160 standard characters. However, if you include non-standard characters in your text, like Chinese characters or emojis for example, then all of a sudden you are allowed only 70 characters per segment. What gives?
This is because text messages are converted to a computer language called character encoding. It's like a phone call; your voice is converted to a transmitting signal—or, encoded—on your end and converted back to sound—or, decoded—on the other end. With texts, your message is encoded using a character set called GSM-7. The character set is suitable only for English and a number of Western-European languages. Languages such as Chinese, Korean, or Japanese, or emojis inserted into the text, must be transferred using the UCS-2 character encoding.
GSM-7 encoding allows for up to 160 characters per segment. UCS-2 encoding allows for up to 70 characters per segment. Messages that include more than 160 standard characters and messages containing at least one non-standard character or emoji that include more than 70 characters will be broken into segments automatically when sending. These segments will then be reassembled into a single message on most handsets. Some older devices or smaller carriers may still display long text messages as separate segments marked with "1/3", "2/3" etc.
Each message segment is considered one "text message" for billing purposes. For example, if you send a message containing 200 standard characters, your monthly total of outbound text messages will be incremented by 2 for each recipient. Note that our carrier adds a User Data Header (this instructs the receiving device on how to assemble messages) to the beginning of the message and is not decoded. Each segment of a multi-segment message can only contain up to 153 GSM-7 characters or 67 UCS-2 characters when there is at least one non-standard character or emoji.
The normal behavior is to use the GSM-7 encoding described above, until one enters a character that is not present in the GSM-7 table (for example, the euro symbol: €). In that case, the whole message gets reencoded using the UCS-2 encoding, and the maximum length of the message sent in a single SMS is immediately reduced.
Use this link to check how your message would be encoded and how many segments would be sent.