SMS Limits
Overview of how Clerk encodes its SMS messages. Encoding is the process of converting data from one form to the other so that it can be translated uniformly.
When you want to send an SMS message you need to understand that there are two different sets of characters that are used by different mobile carriers: GSM-7 and UCS2. When sending SMS messages, Clerk will automatically send messages in the most compact encoding possible. Clerk plans are priced based on your SMS usage (both sent and received).
The character limit for a single SMS message is 160 characters. Nevertheless, most modern phones and networks support concatenation; they can rebuild messages up to 1600 characters. Messages not using GSM-7 encoding are limited to 70 characters.
Example: A 161-character message will be counted as two messages, one with 153 characters and the second with 8 characters.
If you include non-GSM characters, such as an emoji, in SMS messages, those messages have to be sent via UCS-2 encoding. Messages containing any UCS-2 characters are limited to 70 characters.
The maximum number of characters per single message being sent to carriers depends on the encoding used, and the encoding used depends on the content of the message.
For example:
  • A message containing text characters only will be encoded using GSM-7
  • A message containing emojis will be encoded using UCS-2
Message
Type
Characters Used
Encoding
Max characters
Hello - How are you?
Text
GSM Standard
GSM-7
160
😊 👍 🏕️
Emoji
Unicode
UCS-2
70
不是的
Unicode
Unicode
UCS-2
70
Note: We recommend that you check any bulk messages in the Message Segment Calculator before you send them out.

SMS Encoding

Clerk supports both GSM-7 and UCS-2.
GSM-7 is a character encoding standard used for commonly used letters and symbols in many languages.
  • It uses 7 bits to send a single character/symbol on GSM networks. As SMS messages are transmitted as 140 8-bit octets at a time, GSM-7 encoded SMS messages can carry up to 160 characters (140*8/7=160).
  • Refer here for the basic character set for GSM-7.
UCS-2 is a character encoding standard used if a message cannot be encoded using GSM-7 or when a language requires more than 128 characters to be rendered.
  • It uses a fixed-length 16 bits (2 bytes) to send a single character. As SMS messages are transmitted as 140 8-bit octets at a time, UCS-2 encoded messages can carry upto 70 characters {(140*8) / (2*8) = 70}.
  • UCS-2 can encode anything in the Basic Multilingual Plane.
Last modified 10mo ago
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SMS Encoding