Phone carriers measure text messages in character batches called segments. Each segment is 160 or 70 characters long, depending on the message's encoding type. You are billed for each text message segment.
For example, if you send a custom 400-character text message to 100 adorers, each message is 3 segments long, and you are billed for 300 text message segments.
What follows is a broad technical explanation of how a text message's character encoding is determined. If you have any questions about this, please contact us.
Encoding Types
If a text message's characters are constrained to the 8-bit GSM-7 character set, it will be split into 160-character segments.
Otherwise, 16-bit UCS-2 encoding is used, which splits a text message into 70-character segments.
For example, if a message contains characters like Spanish accents, it may use UCS-2 encoding and split into more segments than its English equivalent.
If you love technical reading, see this Wikipedia article.
To preview your text message's encoding and segment length, consider using a tool like this or this.