SMS message length & character limits

SMS messages have character limits. If your message exceeds the limit for a single SMS, Kero automatically divides it into multiple message parts. The number of characters available in each part depends on whether your message uses GSM or Unicode encoding.

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Understanding SMS message parts

An SMS can contain one or more message parts. A short message normally uses one part. When the message exceeds the character limit for a single SMS, it becomes a multipart SMS and is divided into two or more parts. The recipient’s phone normally joins these parts together and displays them as one continuous message. For example: Kero shows the number of Characters and Parts while you compose an SMS.

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GSM character limits

Most standard SMS messages use the GSM character set. A single GSM SMS can contain up to 160 characters. When a GSM message exceeds 160 characters, it becomes a multipart SMS. Each part can then contain up to 153 characters. Some space in each part is reserved for information that allows the recipient’s device to join the message parts together. For example, a GSM message containing 170 characters requires 2 SMS parts.

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Extended GSM characters

Some characters are supported by GSM but require additional space when encoded. Examples include:

• ^
• { and }
• \
• [ and ]
• ~
• |
• €

These characters use two character positions when calculating the encoded SMS length. For example, the text Hello {Alex} contains 12 visible characters but uses 14 GSM character positions because { and } each require two positions.

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Unicode character limits

If your message contains characters that aren’t supported by the GSM character set, it may need to use Unicode encoding. Unicode supports a much wider range of characters and languages. A single Unicode SMS can contain up to 70 characters. When a Unicode message exceeds 70 characters, each multipart SMS part can contain up to 67 characters. Because Unicode has a lower character limit, a Unicode message may use more SMS parts than a similar GSM message.

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What can cause an SMS to use Unicode?

Unicode may be required when your message contains characters that aren’t part of the GSM character set. This can include:

• Characters from some non-Latin writing systems
• Certain accented or special characters
• Typographic punctuation
• Some symbols
• Emojis

Sometimes a character that looks very similar to a standard GSM character can cause the entire message to use Unicode. For example, copying text from a document or website may introduce typographic characters such as curly quotation marks.

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GSM and Unicode compared

The difference becomes more significant as messages get longer. For example, a message containing 200 characters would normally require:

• 2 parts using GSM
• 3 parts using Unicode

These examples assume each character occupies one encoding position or unit.

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Check your message in Kero

When you write an SMS directly in Kero, the SMS Text field shows:

• Characters: The length of your message
• Parts: The number of SMS parts required
• Encoding: Whether the message uses GSM or Unicode

These values update as you type. Use them to check your message before sending.

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Automatically convert to Unicode

When you create an SMS Agent, Kero includes an Automatically convert to Unicode setting. This setting determines how Kero handles characters that are not supported by the standard GSM character set.

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When enabled

Kero uses Unicode encoding when the message contains characters outside the GSM character set. This preserves characters such as emojis, typographic punctuation and characters from other writing systems. However, Unicode messages have lower character limits per SMS part, which may increase the cost of sending your message.

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When disabled

Kero removes characters that are not supported by the standard GSM character set. This can help avoid switching the message to Unicode, but it may also change the content or meaning of your message. For example, an unsupported emoji or typographic character may be removed rather than included in the delivered SMS. You can review this setting when you set up your SMS Agent.

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Keep SMS messages efficient

Before sending a message, check:

• The Characters count
• The Parts count
• Whether Kero shows GSM or Unicode
• Whether unusual characters are increasing the message length
• Whether any unsupported characters have been removed
• Whether the message can be shortened without changing its meaning

For campaigns with large audiences, even one additional SMS part per recipient can significantly increase the total number of SMS messages sent.