GSM and Unicode SMS Length

A single part SMS is not always 160 characters. Depending on the encoding used, a single part message is somewhere between 67 and 160 characters.

Standard SMS Text Messages

Standard SMS text messages are limited to 140 bytes. You can encode 160 7-bit characters in 140 bytes, but even if you are only using simple ASCII characters you are not guaranteed to fit because SMS is encoded in GSM 03.38, not ASCII.

Some characters require two characters to encode. For example ^, €, ~, [ and ]. A message made up only of ~ characters is limited to 80 characters. A message carefully limited to 160 characters may spill into two messages if it includes a single escaped GSM character.

If you use Unicode for languages such as Chinese or Russian, you are restricted to 70 characters for a standard SMS.

Multipart or Concatenated Text Messages

Long multi-part messages need a User Data Header (UDH) so the receiving handset can assemble the parts correctly. This header consumes 6 bytes in each segment, which reduces the space available for the message body.

That leaves 134 bytes, or 153 GSM characters, for each concatenated part. Unicode messages are reduced further.

Our API accepts characters in UCS-2. You can specify the UCS-2 Unicode block as an optional parameter to the API.

Message Length Reference

For messages going through our system the practical limits are:

GSM Encoding

• 1 standard SMS message = up to 160 characters
• 2 concatenated SMS messages = up to 306 characters
• 3 concatenated SMS messages = up to 459 characters
• 4 concatenated SMS messages = up to 612 characters
• 5 concatenated SMS messages = up to 765 characters
• 9 concatenated SMS messages = up to 1,377 characters

UCS-2 Encoding

• 1 standard SMS message = up to 70 characters
• 2 concatenated SMS messages = up to 134 characters
• 3 concatenated SMS messages = up to 201 characters
• 4 concatenated SMS messages = up to 268 characters
• 5 concatenated SMS messages = up to 335 characters
• 9 concatenated SMS messages = up to 603 characters