Message segmentation is the process by which SMS messages longer than 160 characters are split into multiple segments, each billed separately.
Standard GSM Encoding
Using standard GSM-7 character set:
1 segment: 1-160 characters
2 segments: 161-306 characters
3 segments: 307-459 characters
Formula: Subsequent segments hold 153 characters (headers use 7)
Unicode Encoding
When using emojis, non-Latin characters, or special symbols:
1 segment: 1-70 characters
2 segments: 71-134 characters
3 segments: 135-201 characters
Formula: Subsequent segments hold 67 characters
Cost Impact
If your rate is $0.03/segment:
150 character message = $0.03 (1 segment)
165 character message = $0.06 (2 segments)
310 character message = $0.09 (3 segments)
Characters That Trigger Unicode
Emojis
Non-Latin alphabets (Chinese, Arabic, etc.)
Certain punctuation (curved quotes, em dashes)
Some special characters
Best Practices
Use plain text when possible
Avoid smart quotes and special characters
Count characters before sending
Be aware of emoji impact
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