What the Heck is a Messaging Segment?! 🤔

Not all messages are the same. Think of a friend who’s very wordy in their responses and one who you couldn’t pay to send more than one or two words. To you and I, a three paragraph text and “ok” are both a single message. But to the carriers worrying about data transfer costs, they’re certainly not the same 😅

That’s why, back when Nokia ruled the world and Razor flip phones were merely the figments of our imagination, carriers created messaging “segments,” a unit of measurement for a single message comprising 140-byte chunks.

Or, in more practical terms, 160 characters. (fun fact, this is why messages used to come across as “1/n:” they were delivered in segments!)

Message segments are still pervasive, and it’s how Signal House and our upstream partners measure (and bill for) messages.

However, much has changed since the Nokia days; we now can send images, emojis, audio, and more. So, while while 160 characters is still a segment, there’s some nuances at play:

Message Encoding 💽

Generally, messages are encoded with the “GSM 03.38 character set,” but there are other forms of encoding. For example, “UCS2” encoding is used when the characters present are non-GSM characters.

Emojis are an excellent example, and because it takes more bits to encode each character (16 compared to 7), there’s less total characters able to fit in a given message segment. 

How many exactly? Well, a single segment of USC2 encoding is 70 characters; so if you use an emoji in the message, your total segment length will be 70.

Another thing to consider is accented characters. GSM 03.38 includes characters like “ñ,” “à,” and “ö,” but not “á,” “í,” or “ú.”

Finally, “concatenation,” spacing, and “smart quotes” also play a role. 

When multiple segments are delivered, a “user data header” is used to tell the destination how to reassemble the data. This takes up to 6 bytes per message, leaving only 67 characters for USC2 encoding and 153 for GSM-encoded messages.

When using something like a text-editor, you can sometimes encounter “non-GSM spacing” and “smart quotes.” Without adding too much complexity, we recommend using control(command) + shift + v when pasting something you’ve copied–otherwise your message may be encoded with USC2.

Multimedia Messages (MMS) 🎆

MMS segments work very similarly to SMS segments–with the caveat that MMS messages also contain an image, file, video, or audio. Like SMS segments, each MMS segment is 160-characters.

As a general rule of thumb, limiting MMS messages to below 1 MB (1,000 KB) will help ensure deliverability. Each carrier has different size limitations, so your mileage may vary, but in our testing filtering (blocking) generally occurs at 1MB and above (which is why we limit our file size to 1MB on our native applications).