What Is SMS Character Limit?
If you’ve ever typed out a text message and noticed your phone counting down remaining characters, or watched a long message split into multiple parts, you’ve encountered the SMS character limit in action. While it might seem like a simple, almost trivial technical detail, understanding exactly how SMS character limits work, and how they interact with encoding, language, and special characters, is essential for any business sending SMS at scale, since it directly affects both message cost and delivery reliability.
This article explains what the SMS character limit is, why it exists, how encoding changes the limit dramatically, and practical strategies for managing message length effectively.
What Is the SMS Character Limit?
The SMS character limit refers to the maximum number of characters that can be included in a single SMS message segment, as defined by the technical standards underlying SMS. The standard limit is:
- 160 characters for messages using GSM-7 encoding (standard Latin alphabet, numbers, and basic punctuation).
- 70 characters for messages using UCS-2 encoding (used for non-Latin characters, emojis, or certain special symbols).
This limit exists because of a fundamental technical constraint: SMS was originally designed to fit within a fixed 140-byte payload, a limitation dating back to the original GSM standard established in the late 1980s. How many characters fit within those 140 bytes depends entirely on the character encoding used to represent the text.
Why Does SMS Have a Character Limit at All?
SMS was developed as part of the GSM mobile communications standard, designed to transmit short bursts of data efficiently over the signaling channels of early mobile networks, channels that were never intended to carry large amounts of data. The 140-byte payload limit was a deliberate technical constraint to ensure messages could be transmitted quickly and reliably using the very limited bandwidth available on 2G networks at the time.
Despite enormous advances in mobile network technology since SMS was first introduced, the character limit has remained fundamentally unchanged, since SMS’s continued universal compatibility depends on maintaining this original technical specification across all carriers and devices globally.
How Character Encoding Affects the Limit
GSM-7 Encoding: 160 Characters
GSM-7 is a 7-bit character encoding scheme covering the basic Latin alphabet, numbers, and common punctuation, essentially the character set needed for standard English and several other Latin-script languages. Because each character requires only 7 bits rather than a full 8-bit byte, GSM-7 encoding allows 160 characters to fit within the 140-byte (1,120-bit) payload.
UCS-2 Encoding: 70 Characters
UCS-2 is a 16-bit character encoding used when a message contains characters outside the GSM-7 character set, including:
- Non-Latin scripts (Arabic, Chinese, Japanese, Korean, Cyrillic, Hindi, etc.)
- Certain accented Latin characters not included in the extended GSM-7 set
- Emojis and special symbols
Because each character requires a full 16 bits under UCS-2, only 70 characters fit within the same 140-byte payload, less than half the capacity of GSM-7 encoding.
The Hidden Trap: Encoding Switches for the Entire Message
One of the most important technical details businesses need to understand is that encoding is applied to the entire message, not just the specific characters that require it. This means if your message is otherwise entirely in standard English but includes a single emoji, or a customer’s name that happens to include an accented character not in the GSM-7 set, the entire message switches to UCS-2 encoding, cutting your character limit from 160 down to just 70.
This is a common and often costly mistake: businesses inserting a single emoji into an otherwise simple, short message can inadvertently push a message that would have easily fit in 160 characters into requiring multiple UCS-2 segments instead, tripling or quadrupling the cost.
Concatenated SMS: What Happens When You Exceed the Limit
When a message exceeds the single-segment character limit, it doesn’t fail to send, instead, it’s automatically split into multiple segments using a technology called concatenated SMS, covered in more technical depth in dedicated resources on this topic. Each segment includes a small header (User Data Header, or UDH) that allows the receiving device to reassemble the segments into a single, continuous message for the recipient, though this header slightly reduces the character capacity of each individual segment:
- GSM-7 concatenated segments: 153 characters each (instead of 160), due to header overhead.
- UCS-2 concatenated segments: 67 characters each (instead of 70).
Critically, businesses are billed per segment, not per logical message, meaning a message that requires three segments to transmit will typically cost three times as much as a single-segment message, even though the recipient sees it as one continuous text.
Practical Implications for Businesses
1. Cost Management
Since billing is tied directly to segment count, understanding and actively managing character limits has a direct impact on SMS campaign costs, particularly at scale. A business sending millions of messages monthly can see costs multiply significantly if messages routinely spill into multiple segments unnecessarily.
2. Template Design
When designing SMS templates with dynamic merge fields (like customer names or order numbers), businesses need to account for variable-length data that could push a message over the character limit for some recipients even if the template itself, with placeholder text, appears to fit comfortably within a single segment.
3. Localization Challenges
Businesses sending SMS to international audiences, particularly in markets using non-Latin scripts, need to plan for the reduced 70-character UCS-2 limit as a standard consideration, rather than assuming the 160-character GSM-7 limit will apply universally across all markets and languages.
4. Testing for Hidden Encoding Triggers
It’s easy to unintentionally include a character that triggers UCS-2 encoding without realizing it, certain punctuation marks, currency symbols, or even specific quotation mark styles (like curly quotes copied from a word processor) can trigger this shift. Testing message templates through an encoding checker before deployment is an important quality control step.
Best Practices for Managing SMS Character Limits
1. Design for a Single Segment When Possible
Wherever feasible, craft your message content to comfortably fit within 160 characters (or 70 for necessarily non-Latin content), both for cost efficiency and to avoid the slight additional complexity and potential reliability concerns of concatenated messages on some legacy devices.
2. Avoid Unnecessary Emojis and Special Characters
While emojis can boost engagement in some contexts, be aware of the significant character limit trade-off they introduce by forcing UCS-2 encoding, and weigh this cost against the potential engagement benefit for your specific use case.
3. Account for Dynamic Content Length
When using merge fields for personalization, test with your longest realistic data values (like your longest customer name or product title) to ensure the fully populated message doesn’t unexpectedly exceed your intended segment count.
4. Use a Character Counter Tool
Most quality SMS platforms provide a real-time character counter that shows both the current character count and the resulting segment count as you type or as templates are populated, use this actively during message creation rather than assuming length is fine.
5. Prioritize Critical Information First
For messages that may need to span multiple segments regardless (such as detailed instructions), ensure the most critical information appears in the first segment, in case of any delivery or reassembly issues on the receiving end.
6. Consider Alternative Channels for Longer Content
If your message content consistently requires extensive detail that doesn’t fit well within SMS constraints, consider whether a channel better suited to longer or richer content, such as email, RCS, or WhatsApp, might be more appropriate for that specific type of communication.
Conclusion
The SMS character limit, 160 characters for GSM-7 encoding or just 70 for UCS-2 encoding, is a foundational technical constraint rooted in SMS’s original design decades ago, but it remains highly relevant for businesses today due to its direct impact on messaging costs and delivery behavior. Understanding how encoding affects this limit, particularly the often-overlooked way a single special character or emoji can dramatically reduce available space by switching the entire message to UCS-2, is essential knowledge for any business managing SMS communications at scale.
By designing message templates thoughtfully, testing for hidden encoding triggers, and actively monitoring character and segment counts, businesses can keep SMS costs predictable and ensure messages are delivered reliably and efficiently across all markets and devices.
Frequently Asked Questions
Does the SMS character limit include the sender name or number?
No, the character limit applies specifically to the message body content itself, not the sender ID, phone number, or any carrier-added metadata, which are handled separately in the underlying message structure.
Why did my message with no special characters still switch to UCS-2 encoding?
This is often caused by hidden characters that aren’t obviously “special,” such as curly quotation marks or em dashes copied from a word processor, rather than straight quotes or standard hyphens, which are outside the GSM-7 character set. Using a plain text editor or a platform’s built-in encoding checker helps catch these issues.
Can I increase my SMS character limit by paying more?
No, the character limit itself is a fixed technical standard across the entire SMS ecosystem and can’t be increased through pricing; however, you can send longer content through concatenated SMS, which combines multiple segments (each billed separately) to deliver a longer overall message.
Is the character limit the same for all countries?
The underlying technical standard (GSM-7 and UCS-2 encoding limits) is globally consistent, though some carriers or regions may have specific additional restrictions or sender ID requirements that businesses should verify for their target markets.
Does MMS have the same character limit as SMS?
No, MMS (Multimedia Messaging Service) uses a different technical protocol designed for media-rich content and doesn’t share the same strict character constraints as SMS, though it comes with its own considerations around file size limits and more variable carrier support
