SMS character limits and segments: why your 170-character text costs two

An SMS segment holds 160 characters of plain text, or 70 characters if the message contains any character outside the basic GSM alphabet (most emoji, curly quotes, some accented letters). Longer messages are split into segments of 153 or 67 characters and rejoined on the phone. You pay per segment. A 170-character message is two segments; add one emoji to a 100-character message and it becomes two segments as well.

The two alphabets

GSM-7 is the basic set: letters, digits, common punctuation, and a handful of symbols. 160 characters fit in one segment.

UCS-2 is used when any character falls outside that set: emoji, curly (smart) quotes, em-dashes, many accented characters, and symbols like the trademark sign. Then every character costs more space, and 70 fit in one segment.

The whole message switches to UCS-2 if a single character requires it. That is the trap: a message that is 140 characters of plain text plus one emoji is 141 UCS-2 characters, which is three segments.

Concatenation

Messages longer than one segment are split, each piece carries a small header so the phone can reassemble them, and the pieces arrive as one message on modern phones. The header costs space, so multi-part segments hold 153 GSM-7 characters or 67 UCS-2 characters each. Two 153-character pieces give you 306 characters for the price of two segments.

Why it matters at a service business

Reminders go to every appointment. Confirmations go to every booking. A template that runs to two segments doubles the messaging cost across all of them, and carrier fees are per segment. It also matters for delivery: some carriers treat long or heavily segmented messages with more suspicion, and a two-segment message that arrives as two separate texts on an older phone reads badly.

Writing to fit

1. Name the business once, not twice.
2. Use straight quotes and hyphens, not curly quotes or long dashes. Word processors insert the curly kind automatically; paste into a plain editor and check.
3. Skip emoji in templates. One emoji costs you the difference between 160 and 70.
4. Shorten links with a domain you control, so the link is short and recognisable.
5. Write the time as "Thu 10:00" not "Thursday at ten o'clock in the morning".
6. Put the action last and keep it short: "Reply CHANGE to move it."

A booking reminder can carry business name, service, day, time, address and the reschedule instruction in under 160 characters. Most templates that do not fit have a sentence that is not doing anything.

Counting

Your messaging platform should show the segment count as you type a template, and flag when a character has pushed the message into UCS-2. If it does not, paste the template into a segment calculator before saving it. Check your templates once; they are sent thousands of times.

What about MMS

Messages with images are MMS, priced differently and usually higher, with much larger size limits and no segment arithmetic. Useful for sending a photo of the finished job or a map; not the right tool for a reminder.

Frequently asked questions

Do customers see segments?

Usually not; modern phones reassemble them into one message. Occasionally they arrive out of order or as separate texts on older devices, which is one more reason to fit in one.

Does the AI receptionist count segments?

It should, and it should be set to prefer replies that fit in one or two segments. Conversational replies vary; templates are where the discipline pays off.

Are apostrophes safe?

The straight apostrophe is in GSM-7. The curly one is not. Same for quotes.

What Frontiva does here

Frontiva sends SMS through your own Twilio account, so segments and carrier fees follow Twilio's rules, and the plans count SMS segments per month (the pricing page lists the limits). There is no segment counter in the product yet, so check templates in a calculator before you save them. Bookings and automations are where templates are used. See SMS templates for service businesses.