Priority SMS Service: How are SMS Segments Calculated?

When sending an SMS longer than 160 characters, it will be divided into smaller messages for transmission. These large messages are split into 153-character segments, sent individually, and reassembled by the recipient's device. The effective character limit per segment is 153 instead of 160 because each segment needs a data header for correct reassembly.

For example, a 161-character message will be sent as two segments: the first with 153 characters and the second with eight characters.

Including non-GSM-7 characters, like Chinese script or emojis, in SMS messages requires using UCS-2 encoding. Messages with UCS-2 characters can hold up to 70 characters in a single segment. UCS-2 messages exceeding 70 characters are split into 67-character segments.

OnTime bills SMS for each message segment sent. Therefore, if you need to send a 140-character message with one non-GSM character, you can avoid the cost of a second segment by removing that UCS-2 character.