How Unicode affects SMS message segments

An SMS can appear as one message on a customer’s phone while being transmitted as several SMS segments.

The number of segments depends partly on the encoding used. A standard SMS using GSM 7 can contain up to 160 characters. When Unicode encoding is required, that limit falls to up to 70 characters.

For longer messages, the difference becomes even more noticeable.

What are SMS segments

When an SMS exceeds the character limit for a single message, it is split into several segments.

The receiving phone normally reassembles those segments, so the customer sees one continuous message. A small amount of space in each segment is used for the information needed to put the message back together. This reduces the available character count to 153 characters for GSM 7 and 67 for Unicode.

How Unicode changes SMS segmentation

GSM 7 supports a defined set of characters commonly used in SMS. Unicode supports a much wider range of languages, symbols, punctuation, and emojis.

If a message contains even one character that is not supported by GSM 7, the whole message can switch to Unicode encoding.

Consider a message with 150 characters.

Using GSM 7, it can fit into one SMS.

If one character causes the message to use Unicode instead, the same 150 character message requires three SMS segments because a multipart Unicode message contains up to 67 characters per segment.

That is why SMS length is not only about how many characters you type. The characters themselves can change how the message is encoded and segmented.

Which characters can trigger Unicode

Emojis are a common example, but they are not the only characters that can switch an SMS to Unicode.

Smart quotation marks, some accented characters, non Latin scripts such as Arabic or Chinese, and other unsupported symbols can also trigger Unicode encoding.

This can be particularly easy to miss when text is copied from a document, website, or another application.

Some GSM 7 characters can also use additional encoding space without switching the whole message to Unicode. Characters such as €, {, }, [, ], ~, ^, | and \ use the GSM extension table and require an escape character.

Check your SMS before sending

For businesses sending large volumes of SMS, knowing the final number of segments before sending gives teams more control over message length and formatting.

If you are unsure whether a character will trigger Unicode, LINK Mobility’s SMS Length Calculator can help you check the finished message before sending. It identifies the encoding and shows whether the text fits into one SMS or will be split into several segments.

This is particularly useful when messages include emojis, several languages, special characters, or content copied from another source.

The message behind the message

Customers do not need to know whether an SMS uses GSM 7 or Unicode. Businesses sending the message should.

GSM 7 allows more characters per segment, while Unicode makes it possible to communicate using a much broader range of languages and characters. The right choice depends on the message you need to send.

Knowing how encoding affects SMS segments, SMS character limits, and overall SMS message length helps avoid unexpected segmentation and gives teams a clearer picture of how their messages will actually be delivered.