It can double your costs without changing a single visible word. Understanding how SMS length works helps you write messages that stay within a single billable part, keep your costs predictable, and avoid the surprise of a short-looking message being charged as three.
The 160-character rule
A standard SMS holds 160 characters. That figure is not arbitrary. It comes from the ASCII character set most messages use, which covers the letters, numbers and common punctuation used in everyday English.
As long as your message stays within that character set and under 160 characters, it sends as one message and is charged as one message.
What happens when a message goes over 160
A longer message is not rejected. Instead it is split into parts and sent as several linked messages that the recipient’s phone usually reassembles into one. This is called concatenation.
The catch is that splitting adds hidden information to each part so the phone can stitch them back together. That reduces the space available in each part. Once a message runs to multiple parts, each part holds 152 characters rather than 160.
So the counting is not as simple as “twice the length, twice the cost”. The thresholds look like this:
- 1 to 160 characters — 1 message
- 161 to 304 characters — 2 messages
A message of 165 characters — only five over the limit — is still charged as two. Trimming it back under 160 halves the cost for that send, which matters a great deal across a large list.
The emoji trap
This is where costs most often surprise people. The 160-character allowance only applies while your message stays inside the ASCII character set. The moment you add a character outside it, the whole message switches to a different, larger encoding called UCS-2 — and the limit for a single message drops from 160 characters to 70.
A single emoji does this. So does a curly “smart” quote pasted in from a word processor, some accented letters, and certain dashes and symbols. One emoji at the end of a 120-character message can turn a one-part message into a two-part message, because the whole thing is now measured in blocks of 70 rather than 160.
Multi-part messages in this larger encoding hold 67 characters per part rather than 70, for the same reassembly reason as before.
A plain-text message gives you 160 characters per part. Add one emoji or a pasted smart quote and you drop to 70. If you want the reach of 160 characters, keep the message in plain text and type your punctuation directly rather than pasting it in.
Why the link in your message counts too
A web link is made of characters like any other text, so it consumes your allowance. A long link can eat 40 or 50 characters on its own. Because SMS has no way to hide a link behind a word — the full address has to appear as text — a long URL can be what pushes a message into a second part.
A link shortener helps by turning a long address into a short one, buying back characters for your actual message. Keep in mind that you are then relying on the recipient’s phone to recognise the shortened address as a tappable link.
How to keep messages to a single part
- Aim for 160 characters or fewer, and count the link as part of that. Our online SMS tools show a count of characters and message parts, so you know what you will be billed for before you send.
- Write in plain text. Avoid emoji and special symbols unless they genuinely earn their place.
- Type punctuation directly rather than pasting from a document, to avoid smart quotes and unusual dashes.
- Shorten long links so the address does not consume your message.
- If a message genuinely needs to be longer, know before you send that it will be charged as more than one.
None of this means a longer or emoji-containing message is wrong. Sometimes the extra length or the emoji is worth the cost. The point is to make that a decision you take deliberately, rather than a charge you discover afterwards.