A single SMS holds 160 characters with standard GSM-7 encoding, or 70 characters when it contains Unicode (UCS-2). Anything longer splits into concatenated segments of 153 or 67 characters each — and each segment bills separately.
That one rule explains most surprises in SMS sending: why your message length suddenly drops, why one emoji turns a 160-character text into two, and why a long message costs more to send. Here is the full reference, with the math and the sources behind it.
SMS character limit and length: quick reference
Use this table whenever you need the exact SMS length figures. The numbers come from the GSM 03.38 / 3GPP TS 23.038 standard.
| Encoding | Single SMS | Per segment (concatenated) | Bytes per segment |
|---|---|---|---|
| GSM-7 (standard text) | 160 characters | 153 characters | 140 |
| UCS-2 / Unicode (emoji, accents, non-Latin) | 70 characters | 67 characters | 140 |
Every SMS segment carries the same 140-byte payload — the usable space in each message. The encoding decides how many characters fit inside those 140 bytes — and that is the whole story of SMS length.
What is the SMS character limit?
The SMS character limit is 160 characters for a single message using GSM-7, the default 7-bit alphabet for text messaging.
The limit traces back to the payload size. A single SMS payload is limited to 140 bytes, which equals 160 characters when encoded with the 7-bit GSM-7 alphabet, per the GSM 03.38 / 3GPP TS 23.038 standard. The math is direct: 140 bytes × 8 bits, divided by 7 bits per character, equals 160 characters.
So the 160-character SMS limit is not random. It is the most characters you can pack into 140 bytes at 7 bits each.
Why do some texts only allow 70 characters?
Because the moment your message includes a character outside the GSM-7 set, the whole message becomes a Unicode SMS — and the limit drops from 160 to 70.
When an SMS contains characters outside the GSM-7 alphabet, it uses UCS-2 (Unicode) encoding and is limited to 70 characters in a single 140-byte segment, again per the GSM 03.38 standard. Unicode characters need 16 bits each instead of 7, so far fewer fit into the same 140 bytes.
This is the single biggest cause of unexpected SMS length. One emoji, one curly quote, or one accented letter — and your comfortable 160-character message becomes a 70-character one.
Which characters force Unicode encoding?
Any character not in the GSM-7 alphabet — a non-GSM character — forces the whole message into Unicode (UCS-2) and cuts your limit to 70 characters. The most common culprits:
- Emoji — every emoji is a Unicode character. A single 😊 triggers UCS-2.
- Curly or smart quotes —
“ ” ‘ ’(the styled quotes word processors auto-insert) are non-GSM. Straight quotes" 'are safe. - Accented letters — é, ñ, ü, å, ç and similar. (A small set of accented letters is in GSM-7; most are not.)
- Non-Latin scripts — Arabic, Chinese, Cyrillic, Hindi, Amharic and other scripts are all Unicode.
- Special typographic characters — the em dash (—), ellipsis (…), and some bullet and currency symbols.
The GSM-7 set itself covers the basic Latin letters, digits, common punctuation, and a handful of European accented characters. Stay inside it and you keep all 160 characters. Step outside it — even once — and the entire message recodes to Unicode at 70.
A practical tip: a stray smart quote pasted from a document is the most common silent cause. Replace it with a straight quote and you reclaim 90 characters.
How does SMS message segmentation work?
When your message runs past the single-segment limit, it does not get cut off. It splits into a concatenated (multipart) SMS — several segments the recipient’s phone stitches back into one message.
Concatenation costs you a few characters per segment. In a concatenated (multipart) SMS, each segment carries 153 GSM-7 characters or 67 UCS-2/Unicode characters, because the User Data Header consumes part of each segment’s payload. A long message simply splits into as many segments as it needs, and each segment is billed separately.
The User Data Header is a small block of metadata that tells the phone how to reassemble the parts. It takes up room inside the 140 bytes, which is why per-segment capacity falls from 160 to 153 (GSM-7) and from 70 to 67 (Unicode).
The takeaway for anyone sending at scale: segments, not messages, are the unit that matters. A 320-character GSM-7 message is two segments. The same message with one emoji becomes Unicode — and at 67 characters per segment, 320 characters now needs five.
Why is my message being sent (and billed) as 2 or more messages?
Your message crossed the single-segment limit. Once it does, the carrier splits it into concatenated segments, and most platforms bill per segment.
Two things commonly trigger this:
- Length — your text simply ran past 160 (GSM-7) or 70 (Unicode) characters.
- Encoding — a Unicode character pulled the limit down to 70/67, so a message you expected to fit in one segment now needs two or more.
This is where SMS length becomes a real cost question. Multi-segment messages cost more to send than single-segment ones, so tight, GSM-7-only copy keeps both your character count and your sending costs down. For current rates, see Arkesel pricing.
A segment-aware sending platform helps here: it shows you the live segment count as you write and warns when a stray Unicode character is about to double your send. The Arkesel SMS Platform handles encoding detection and segmentation automatically, so you reach customers reliably without surprise multi-segment costs.
SMS length quick FAQ
How many characters are in one SMS?
160 characters with GSM-7 encoding, or 70 characters with Unicode (UCS-2).
What is the maximum length of a concatenated SMS?
There is no fixed maximum. A long message splits into multiple segments of 153 (GSM-7) or 67 (Unicode) characters each, and each segment is billed separately.
Why does my SMS character limit drop to 70?
Your message contains a non-GSM character — an emoji, a curly quote, an accent, or a non-Latin script — which switches the whole message to Unicode encoding.
Does an emoji really change the SMS length?
Yes. A single emoji recodes the entire message to Unicode, dropping the limit from 160 to 70 characters and often turning one segment into two.
How many characters per segment in a multipart SMS?
153 for GSM-7 and 67 for Unicode — slightly fewer than a single message because the User Data Header reserves space to reassemble the parts.
Send SMS that scale, without surprise segments
Knowing the SMS character limit is step one. Sending reliably at scale — with automatic encoding detection, live segment counts, and real-time delivery tracking — is what keeps your costs predictable as your volume grows.
Explore the Arkesel SMS Platform to reach customers instantly with messages that land reliably. Building SMS into your own product? The Arkesel SMS API for developers gives you segment-aware sending and delivery tracking through a clean REST integration. For deeper technical reading, see our guides on SMS delivery reports and tracking and the bulk SMS API integration guide.
