Messages containing Regular English Text can contain up to 160 characters in order to be considered as one segment.
Messages containing Special characters such as emojies, €, text in a language other than English can contain up to 70 characters in order to be considered as one segment.
If you send messages containing more than one segment, the segment calculation will vary due to the message concatenation (allowing messages to be received on the recipients’ phones as one long message). Detailing available here:
When typing your message on the Platform you will be able to see at all times the number of accumulated characters you have as well as the total of segments reached: