What is a Segment?

SMS Character Limit

A single SMS message technically supports up to 160 characters, or up to 70 if the message contains one or more Unicode characters (such as emoji or Chinese characters).

However, modern phones and mobile networks support message concatenation, which enables longer messages to be sent. Messages longer than 160 characters are automatically split into parts (called "segments") and then re-assembled when they are received. Message concatenation allows you to send long SMS messages, but this increases your per-message cost, because SMS are billed per segment.

The 160-character limit is for messages encoded using the GSM-7 character set. Messages not encoded with GSM-7 are limited to 70 characters.

Nollab recommends keeping messages that are no more than 300 characters to ensure the best deliverability and user experience.

SMS message length and character encoding

When you send an SMS message containing more than 160 characters, the message is split into smaller messages for transmission. Large messages are split into 153-character "segments" and sent individually, then re-assembled by the recipient's device. The effective character limit per segment is 153 rather than 160, because a data header must be included with each segment to ensure correct re-assembly.

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

If you include non-GSM-7 characters, such as Chinese script or emoji, in SMS messages, those messages have to be sent using the UCS-2 encoding. Messages containing one or more UCS-2 characters can contain up to 70 characters in a single, non-segmented message. UCS-2 messages of more than 70 characters will be split into 67-character segments.