Calculation of SMS segments

How do SMS and MMS message limits work with SOMUM?

Understanding message limits is essential for effective communication. Here’s how SMS and MMS messages are calculated with SOMUM.

Understanding SMS segment calculation

SMS billing depends on the length of your message and the presence of special characters.

  1. For a standard SMS (without special characters)

Containing only the following characters:

  • \n (line break)
  • @£$¥èéùìòÇØøÅåΔ_ΦΓΛΩΠΨΣΘΞ^{}[~]|€ÆæßÉ!\”#¤%&\'()*+,-./0123456789:;<=>?¡ABCDEFGHIJKLMNOPQRSTUVWXYZÄÖÑܧ¿abcdefghijklmnopqrstuvwxyzäöñüà

If your message does not contain any special characters (such as ç, “, ”, —, ©, ®, or emoticons/emojis):

  • 1 to 160 characters: The message counts as 1 SMS per contact.
  • More than 160 characters: Each additional 153 characters counts as one additional SMS.
    • Example: A message of 268 characters will be billed as 2 SMS (153 + 115 remaining). A message of 307 characters will count as 3 SMS (153 + 153 + 1 remaining).
  1. For an SMS with special characters

If your message contains at least one special character (such as ç, “, ”, —, ©, ®, or any emoticon/emoji):

  • 1 to 70 characters: The message counts as 1 SMS per contact.
  • More than 70 characters: Each additional 67 characters counts as one additional SMS.
    • Example: A 128-character message (with special characters) will be billed as 2 SMS messages (67 + 61 remaining). A 135-character message (with special characters) will count as 3 SMS messages (67 + 67 + 1 remaining).

Why does the maximum size per segment decrease?

When your message exceeds the limit for a single SMS, it is automatically divided into several parts, called segments. In order for the recipient’s phone to reconstruct the complete message in the correct order, each segment includes invisible technical information (such as “part 1 of 2”). This information takes up a small amount of space, which is why the usable capacity of each segment decreases (from 160 to 153 characters, or from 70 to 67 characters) as soon as the message requires more than one segment.

Characters that require special encoding (Unicode) or count as two characters

Using certain specific characters in French may reduce the limit of your SMS or cause them to count as two characters.

  • Characters that force Unicode encoding (70 characters max per SMS):

    • Accented uppercase letters not in standard GSM 7-bit: À, Ê, Ë, Î, Ï, Ô, Ù, Û, Ü.
    • Specific accented lowercase letters: œ, â, ê, î, ô, û, ë, ï, ü.
    • Typographic symbols and punctuation: € (Euro symbol), French quotation marks («, », “, ”, ‘, ’), em dash (—), copyright/trademark symbols (©, ®), most non-standard mathematical or monetary symbols.
    • All emojis (😄, 👍, ❤️, 🌍, etc.).
    • Characters from other alphabets (Cyrillic, Arabic, etc.).
  • Characters that count as double in GSM 7-bit (reduce available space):

    • ^ (Caret alone)
    • { , } (Curly braces)
    • [ , ] (Square brackets)
    • € (Euro Symbol)
    • ~ (Tilde)
    • \ (Backslash)
    • | (Vertical bar)

To stay within standard encoding (and benefit from 160 characters per SMS), only use basic Latin alphabet letters, numbers, simple punctuation, and common accents (é, è, à, ù, ç, Ç, É, _).

While we do submit your message payloads to the carriers using Latin-1 encoding, which has broad support for French/accented characters, some carriers convert the final message payload to GSM for delivery to the handset. This can limit the number of supported French/accented characters.

Understanding MMS (Multimedia Messaging Service) Limits

MMS is much more than a simple SMS. It allows you to send images, videos, and audio files. Its rules are different and less focused on character count.

  1. The Primary Constraint: Total Message Size

An MMS is transferred via the mobile data network, meaning its main constraint is the combined size of all its content (media and text).

  • Typical limit: between 300 KB and 1 MB. Most mobile operators impose a global size limit. To ensure the best compatibility across all networks and devices, aim for a size between 300 KB and 600 KB.
  • Multimedia content is king: Images, videos, and audio files take up the most space. A high-resolution image or a short video can quickly increase your message size and reach this limit.
  1. Text Character Limit (More Generous)

While the total file size is the dominant factor, the text within an MMS still has a limit, but it’s much more generous than an SMS, typically up to 1600 characters.

  • Unlike SMS, MMS uses a broader data encoding. You can include emojis or special characters without drastically reducing the text limit, as long as the overall message size remains within the boundaries.
  1. The Impact of Multimedia on Text

The text “limit” in an MMS is mostly an indirect consequence of the total size limit. If you include a very large image or a long video, less space will be available within the 300 KB to 1 MB allowance for text. This will then force you to condense your written message. The system will prioritize media: if the MMS exceeds the allowed size, the media will be compressed or resized first. In extreme cases, the message might not be delivered or the media replaced by a web link.

  1. Variations Between Operators and Devices

The exact MMS limits can vary slightly depending on:

  • Mobile operators (each provider has its own network configurations).
  • Mobile devices (older phones, for example, might have difficulty receiving very large MMS).

Geographical location (MMS capabilities and limits can differ by country).