GSM-7 or UTF-16: How Encoding Types Affect SMS Character Limits

SMS remains a highly popular medium. Its key advantage: universality. Anyone with a mobile phone can receive an SMS, whereas app-based messaging requires both sender and recipient to have the same application installed. Despite its popularity, SMS does come with a few limitations.

A limit on characters and possibilities

Widely used for marketing campaigns and relatively inexpensive, the short message service is inherently designed to be brief. In fact, its encoding more precisely determines its maximum character count.

No computing without encoding

What exactly is encoding? Everything that exists digitally — text, photos, images, video, or audio — is translated into lines of code.

Each character in our alphabet, every number and accent, is written in code. In the early days of computing, the first American standard using hexadecimal characters emerged: ASCII codes. Then, a long process of universalizing these codes took place, offering greater flexibility. Complex characters and the alphabets of other cultures that could not previously be rendered in ASCII are now supported by standards shared worldwide.

SMS: 140 bytes, but a variable number of characters

An SMS message is limited to 140 bytes. Depending on how it is encoded, this represents a variable number of characters. The encoding type predominantly used in the Western world is currently GSM-7. Its advantage is that it uses only 7 bits per character, allowing a maximum of 160 characters per message (140/8*, since one byte contains 8 bits).

However, it has a few limitations: while it supports Latin alphabets, it struggles considerably with non-Latin languages. The encoding becomes unwieldy to manage, and a different format is then preferred.

> Voir la liste des caractères non pris en charge sur SMS Partner depuis la plateforme ou l’API SMS.

UTF-16, better suited for non-Latin languages

When corresponding via international SMS, the alphabet may sometimes need to change. For example, in Chinese, Arabic, or languages using Cyrillic characters, the UTF-16 format comes into play. It is heavier, since at least 2 bytes are required to encode a single character. In UTF-16, an SMS will therefore never exceed 70 characters (140/2). It also allows you to include emoticons in your messages (and that really does make a difference…)

Looking for a tool to count your characters in GSM-7 or UTF-16 format?

Discover our character counter

The encoding dilemma: richer content, but shorter messages?

Why do we continue to rely primarily on GSM-7? For obvious cost reasons. Even though individuals today benefit from unlimited plans that make the price of a single SMS invisible, bulk sending has a cost, and doubling the message size doubles the cost.

While SMS messages are limited to 160 or 70 characters, sending longer texts is perfectly possible. Seamlessly, multiple SMS messages are combined. The user has the impression of sending or receiving just one, but in reality up to 800 characters can be sent in GSM-7 and 400 in UTF-16 through the aggregation of multiple SMS messages.

This is why it is advisable to check the actual size of the messages planned for your SMS communication campaigns . Using UTF-16 more than doubles the cost of your campaign.