Troubleshooting > Message Size

Short Explanation:

For single SMS messages the maximum message size is:

•160 characters for 7-bit (US, English) characters

•140 characters for 8-bit (European, Western European) characters

•70 characters for 16-bit (Arabic, Chinese, Korean, Japanese or Cyrillic (e.g. Russian, Serbian, Bulgarian)) characters

For long (multipart) SMS messages the maximum message size for each part is:

•153 characters for 7-bit (US, English) characters

•133 characters for 8-bit (European, Western European) characters

•67 characters for 16-bit (Arabic, Chinese, Korean, Japanese or Cyrillic (e.g. Russian, Serbian, Bulgarian)) characters

Detailed/Technical Explanation:

Transmission of short messages between the SMSC and the handset is done whenever using the Mobile Application Part (MAP) of the SS7 protocol. Messages are sent with the MAP mo- and mt-ForwardSM operations, whose payload length is limited by the constraints of the signaling protocol to precisely 140 octets (140 octets = 140 * 8 bits = 1120 bits). Short messages can be encoded using a variety of alphabets: the default GSM 7-bit alphabet (see GSM 03.38 for details), the 8-bit data alphabet, and the 16-bit UTF-16 alphabet.[1] Depending on which alphabet the subscriber has configured in the handset, this leads to the maximum individual Short Message sizes of 160 7-bit characters, 140 8-bit characters, or 70 16-bit characters (including spaces). Support of the GSM 7-bit alphabet is mandatory for GSM handsets and network elements,[1] but characters in languages such as Arabic, Chinese, Korean, Japanese or Cyrillic alphabet languages (e.g. Russian, Serbian, Bulgarian, etc) must be encoded using the 16-bit UTF-16 character encoding (see Unicode). Routing data and other metadata is additional to the payload size.

Larger content (Concatenated SMS, multipart or segmented SMS or "long sms") can be sent using multiple messages, in which case each message will start with a user data header (UDH) containing segmentation information. Since UDH is inside the payload, the number of characters per segment is lower: 153 for 7-bit encoding, 133 for 8-bit encoding and 67 for 16-bit encoding. The receiving handset is then responsible for reassembling the message and presenting it to the user as one long message. While the standard theoretically permits up to 255 segments,[2] 6 to 8 segment messages are the practical maximum, and long messages are often billed as equivalent to multiple SMS messages. See Concatenated SMS for more information. Some providers have offered length-oriented pricing schemes for SMSs, however, the phenomenon is disappearing.

[1] 3GPP TS 23.038, Alphabets and language-specific information.
[2] Ian Groves: "Mobile Systems", page 70, 79, 163-166. Chapman & Hall, 1998.

Source Wikipedia (6/11/2009): http://en.wikipedia.org/wiki/SMS