Salesforce Digital Engagement: SMS Message Length Limits and Unicode Encoding Impact

When attempting to send an SMS, users may encounter the following error message:

"Can't send this message because the message body is too large."

This error indicates that the message has exceeded the platform's maximum character or segment limit. While the standard limit for an SMS Long Code channel is 912 characters, the actual limit is determined by the encoding type used for the message.

GSM vs. Unicode

SMS messages are sent in "segments." The number of characters allowed per segment depends on the characters included in your message:

1. GSM-7 Encoding (Standard Text): * Used for standard Latin letters, numbers, and basic punctuation.

   • Segment Capacity: 152 characters.

   • Maximum Limit: 912 characters (6 segments × 152 characters).

2. Unicode Encoding (Emojis & Special Characters): * If a message contains even one non-GSM character—such as an emoji, a special symbol, or a "curly" quotation mark (’)—the entire message is converted to Unicode.

   • Segment Capacity: 66 characters.

   • Maximum Limit: 396 characters (6 segments × 66 characters).

Example Scenario

Consider a message that contains 638 total characters.

• Scenario A (Failure): The message includes a curly apostrophe (e.g., "We’re"). Because this is a Unicode character, the message requires approximately 10 segments. Since the platform limit is 6 segments, the message fails with the "Body Too Large" error.

• Scenario B (Success): The same message is edited to use a standard straight apostrophe (e.g., "We're"). The message now uses GSM encoding, requires only 5 segments, and sends successfully.

To ensure successful delivery, we recommend the following:

• Avoid Special Characters: Be cautious when copying text from word processors (like Microsoft Word), as they often auto-format "straight" quotes into "curly" quotes.

• Limit Emojis: Adding an emoji will immediately reduce your total character limit from 912 to 396.

• Use a Segment Calculator: Before finalizing a template, test your text using an external segment calculator to see how it will be encoded: https://twiliodeved.github.io/message-segment-calculator/