The SMS character limit is 160 characters for standard GSM-7 encoding and 70 characters for Unicode (UCS-2) encoding. One emoji, curly quote, or accented character silently switches your entire message to Unicode mode, cutting your limit to 70 characters, and messages longer than one segment are split into concatenated parts billed separately by most carriers and gateways.
That single sentence contains the most expensive misunderstanding in SMS marketing. A 161-character message doesn't cost a little more, it costs double. A message with one emoji can cost triple what you expected. This guide explains exactly how the 160-character limit works, how segments and billing really function, and how to design message templates that keep your costs predictable.
Why Is the SMS Limit Exactly 160 Characters?
The 160-character limit is not a design choice, it's a technical constraint inherited from the 1980s. When GSM engineers designed SMS, they allocated 140 octets (1,120 bits) of payload space per message.
The GSM-7 alphabet encodes each character in 7 bits. Do the math: 1,120 ÷ 7 = 160 characters. That's the entire story. The limit exists because a Finnish engineer named Friedhelm Hillebrand determined in 1985 that 160 characters was enough for most short messages (he reportedly counted characters on postcards and telex messages), and the 140-octet signaling channel space fit it perfectly.
Unicode characters need 16 bits each (UCS-2 encoding). Same 1,120 bits ÷ 16 = 70 characters. The limit shrinks because each character takes more than twice the space.
GSM-7 vs Unicode: The Two Encodings That Control Your Limit
Every SMS you send uses one of two encodings, and the encoding is decided by a single rule: if every character in your message exists in the GSM-7 alphabet, you get 160 characters. If even one character falls outside it, the entire message switches to Unicode and your limit drops to 70.
The GSM-7 alphabet covers basic Latin letters, digits, and common symbols:
| Category | Characters included |
|---|---|
| Letters | A-Z, a-z |
| Digits | 0-9 |
| Common symbols | space ! " # % & ' ( ) * + , – . / : ; < = > ? @ $ £ ¥ |
| Special | € [ ] { } ~ ^ and vertical bar (these use escape sequences, counting as 2 characters each) |
Characters that force Unicode mode, the usual suspects:
| Character type | Examples | Why it matters |
|---|---|---|
| Emoji | 🎉 😀 👍 | The #1 cause of surprise billing |
| Curly/smart quotes | " " ' ' | Auto-inserted by Word, Google Docs, iPhones |
| Long dashes | em dash and en dash | Common in professionally written copy |
| Accented letters | é ñ ü ç | Frequent in Spanish, French, Portuguese marketing |
| Non-Latin scripts | Arabic, Chinese, Hindi, Cyrillic | Entire message becomes Unicode |
The curly-quote trap deserves emphasis. Marketers routinely draft messages in Google Docs or Word, which auto-convert straight quotes to curly quotes. Paste that copy into your SMS platform and your 150-character message just became a 3-segment Unicode message costing 3×. Always paste through a plain-text editor, or better, check every message with a free SMS character counter before sending.
Try it free: Free SMS Character Counter
Use our free sms character counter right in your browser, no signup needed.
Concatenated SMS: What Happens After 160 Characters
When your message exceeds one segment, your phone and the carrier split it into multiple SMS parts and reassemble them on the recipient's device. This is called concatenated SMS (or long SMS), and it works invisibly, the recipient sees one long message.
But there's a catch: each part needs a small header (UDH, User Data Header) so the receiving phone knows how to reassemble them. That header eats 7 characters per segment:
| Encoding | Single message | Concatenated (per segment) |
|---|---|---|
| GSM-7 | 160 characters | 153 characters |
| Unicode (UCS-2) | 70 characters | 67 characters |
So a 161-character GSM-7 message becomes two segments (153 + 8), and you are billed for two messages. A 200-character message is two segments. A 307-character message is three. The billing boundary table:
| Your message length (GSM-7) | Segments billed | Your message length (Unicode) | Segments billed |
|---|---|---|---|
| 1-160 | 1 | 1-70 | 1 |
| 161-306 | 2 | 71-134 | 2 |
| 307-459 | 3 | 135-201 | 3 |
| 460-612 | 4 | 202-268 | 4 |
Illustrative example: a 165-character promotional message with one emoji (🎉) at the end. The emoji forces Unicode mode. At 165 Unicode characters, that's 3 segments (67 + 67 + 31) instead of the 2 segments the marketer expected. At $0.0075 per segment, that single emoji raised the cost per recipient from $0.015 to $0.0225, a 50% increase across a 100,000-recipient campaign equals $750 wasted on one emoji.
How Emoji and Special Characters Multiply Your SMS Bill
Carriers and SMS gateways bill per segment, not per message. This is where the character limit becomes a budget issue:
- A 150-character GSM-7 message = 1 segment = 1× cost
- The same message + 1 emoji = Unicode, 151 characters = 3 segments = 3× cost
- A 320-character GSM-7 message = 3 segments = 3× cost
MMS is sometimes suggested as an alternative for long content, but MMS typically costs 3 to 5 times as much as a single SMS segment and has its own deliverability quirks. For text-only content, staying within segment boundaries is almost always cheaper.
Practical rules to control costs:
- Audit every template with a character counter that detects encoding before you schedule a campaign.
- Ban smart quotes and em dashes in your SMS copy guidelines, use straight quotes and hyphens.
- Decide on emoji deliberately. One emoji in a short message is fine if you budget 2 segments. Accidental emoji are the problem.
- Design to segment boundaries. If your message is 165 characters, cutting 5 characters saves 50% of the cost. If it's 310 characters, cutting to 306 saves a full third.
- Put links early. If you must trim, URLs and CTAs should survive the cut, trim adjectives, not the call to action.
Designing SMS Templates Within the Limit
The character limit should shape how you write, not just how you're billed. High-performing SMS templates share a structure that fits comfortably in one segment:
- Hook (first 20 characters): the offer or reason to keep reading, most phones preview this in notifications.
- Body: one clear idea, plain words, no filler.
- CTA + link: short link (use a shortener), clear verb.
Example of a 132-character, single-segment template:
"FLASH SALE: 25% off all phone accessories today only. Shop now: smsmkt.co/sale25 Reply STOP to opt out"
That's 118 characters, GSM-7 clean, one segment. Compare with a version that drifts over the edge, adding "Hurry, this exclusive deal ends at midnight tonight! 🎉" pushes it past 160 into two segments and Unicode into three. Same offer, triple the cost.
For templates you reuse across campaigns, also remember 10DLC campaign registration, carriers review your sample messages during vetting, and messages that look like they'll exceed segment expectations can raise questions.
Frequently Asked Questions
Why is the SMS character limit 160 and not more?
The limit comes from the original GSM specification: each SMS carries 140 octets (1,120 bits) of payload. The GSM-7 alphabet uses 7 bits per character, giving exactly 160 characters. It's a hardware-era constraint that the entire mobile ecosystem standardized around.
Does the 160-character limit include spaces?
Yes. Spaces, line breaks, and punctuation all count as characters toward the limit. Every keystroke counts.
How many characters is a Unicode SMS?
70 characters for a single Unicode (UCS-2) message, or 67 characters per segment for concatenated Unicode messages. Any single emoji, curly quote, or non-Latin character switches the whole message to Unicode.
Am I charged extra when a message splits into two segments?
Yes, with nearly all carriers and SMS gateways: each segment is billed as a separate message. A 2-segment message costs twice as much as a single-segment message. Always check your provider's per-segment pricing, see our bulk SMS API comparison for how providers differ.
Do emojis really increase SMS cost?
They can. One emoji forces the entire message into Unicode encoding (70/67-character limits instead of 160/153). A message that was 1 segment in GSM-7 can become 3 segments in Unicode, tripling the cost. Use emoji intentionally and budget the extra segments.
What's the maximum length of a concatenated SMS?
Technically up to 255 segments, but most carriers and gateways cap concatenated messages at 6 to 10 segments (around 918 to 1,530 GSM-7 characters). Beyond that, messages may be rejected or split unpredictably. For marketing, anything over 3 segments should probably be shortened or moved to another channel.
GSM-7 character encoding reference Unicode character database SMS API messaging concepts