sms delivery Archives

TL;DR:

SMS character limits define the maximum payload size per text, ensuring proper routing, carrier compliance, clear messaging, and predictable delivery costs.

Standard Cap: GSM-7 encoding allows 160 characters per SMS.
Unicode Impact: Emojis and special symbols reduce limits to 70 characters.
Segment Splitting: Multi-part messages cost extra due to underlying header data.
Cost Efficiency: Concise copy prevents unintended segment costs and protects ROI.

Understanding how SMS character limits work can help you write messages that are clear, efficient, and less likely to be split into multiple segments.

Every mobile network globally relies on standardized character constraints, which dictate exactly how your copy gets processed and delivered. When a message exceeds these parameters, carriers automatically divide the text, potentially doubling or tripling your delivery costs without warning.

This guide covers the key factors that affect SMS length and how to make the most of the space available. By mastering message encoding and payload limits, you can protect your marketing ROI and deliver clean, high-impact messages every time.

SMS Character Count Explained

Every mobile network globally relies on standard protocols to handle message payloads. A single, standard SMS using standard character encoding has a hard limit of 160 characters. This default encoding is known as GSM-7 (Global System for Mobile Communications), which includes basic Latin letters, numbers, and a selection of common symbols.

Encoding Type	Standard Limit	Concatenated Segment
GSM-7	160 characters	153 characters / SMS
Unicode (UCS-2)	70 characters	67 characters / SMS

When you insert a non-standard character–such as an emoji, an accented letter, or non-Latin script–the entire message shifts from GSM-7 to Unicode (UCS-2) encoding. Because Unicode characters require more data per symbol, the single-message limit instantly drops from 160 down to 70 characters.

If your message exceeds the standard character limit, mobile carriers do not block it; instead, they split it into multiple text segments. However, these “concatenated messages” require extra routing headers (User Data Headers or UDH) to ensure the recipient’s handset seamlessly reassembles the text. These headers take up space, reducing the available payload per segment:

GSM-7 Multi-part: Each segment is capped at 153 characters (rather than 160).
Unicode Multi-part: Each segment is capped at 67 characters (rather than 70).

For example, a 170-character message in GSM-7 standard text won’t fit into one SMS. It gets split into two segments (153 characters + 17 characters), and you are billed for two separate messages.

Knowing your exact SMS character count ensures you avoid paying double for just a few extra characters.

Best Practices to Maximize SMS Character Count

Optimizing your messaging strategy requires balancing clear communication with structural efficiency. Even minor tweaks to formatting or phrasing can prevent unnecessary segment splits, lowering campaign costs while ensuring deliverability.

Use GSM-7 characters whenever possible.
Stick to the standard alphabet, standard numbers, and basic punctuation. Avoiding obscure symbols ensures your message stays at the 160-character baseline per segment.
Avoid unnecessary emojis and special characters.
Adding a single emoji converts the entire message payload to Unicode, instantly reducing your standard limit from 160 to 70 characters. If you must use emojis, ensure the high engagement rate justifies the extra segment costs.
Keep messages concise and focused.
Stick to a single clear value proposition and one specific call-to-action (CTA). Cut out extra adjectives or redundant details that do not add immediate value to the reader.
Use abbreviations sparingly.
While shortening words saves space, overusing “textspeak” or non-standard shorthand undermines brand authority and alienates readers. Stick to universally understood terms when necessary.
Check text message characters before sending.
Always run your draft through a character counter or SMS preview tool within your dashboard to detect hidden Unicode formatting or unexpected segment splits before broadcasting.
Minimize unnecessary spaces and line breaks.
Multi-line formatting adds extra hidden characters to your total count. Use single spaces and concise punctuation to separate ideas cleanly without inflating payload size.
Plan longer messages to reduce the number of SMS segments.
If a message exceeds 160 characters, target the 306-character mark (two GSM-7 segments) rather than spilling into a third segment by just three or four extra letters.
Use Unicode only when necessary.
Reserve Unicode for instances where specific non-Latin character sets (such as Cyrillic, Chinese, or Arabic) or critical brand elements are strictly required for communication.

By applying these structural refinements, you can consistently deliver high-impact copy while keeping campaign overheads fully optimized.

Take Control of Your SMS Deliverability and Costs

Mastering SMS character limits isn’t just about trimming unnecessary words—it’s about taking complete control over your marketing ROI, routing efficiency, and delivery success. A single stray emoji or hidden formatting error can silently multiply your messaging costs, transforming a straightforward broadcast into an expensive multi-part payload.

If you’re looking for a reliable, transparent partner to power your customer communications, consider Semaphore. Designed to bypass complex telecom contracts and cumbersome setups, our messaging platform offers continuous payload queueing, clear message logging, and instant API integration.

Explore Semaphore’s flexible SMS solutions today to keep your messaging scalable, compliant, and cost-efficient.

FAQ

What is the character limit for a single SMS?

A single standard SMS contains up to 160 characters using GSM-7 encoding. If your message contains non-standard symbols or emojis, the single-message limit drops to 70 characters due to Unicode encoding.

What is the difference between GSM-7 and Unicode SMS?

GSM-7 uses standard 7-bit encoding designed for basic Latin letters, numbers, and common punctuation. Unicode (UCS-2) uses 16-bit encoding to support non-Latin scripts, accented letters, and modern emojis, taking up significantly more data per character.

Why do emojis affect SMS character limits?

Emojis are complex 16-bit symbols that force mobile carriers to switch the entire message payload from GSM-7 to Unicode encoding. This encoding shift instantly reduces your available payload from 160 down to 70 characters per text.

Which characters can reduce the SMS character limit?

Emojis, non-Latin alphabets, and special accented characters drop your text cap to 70 characters. Additionally, extended GSM-7 symbols like brackets [ ], braces { }, or the euro sign € count as two characters each.

How are longer SMS messages split into segments?

Messages exceeding single-text limits are split into multi-part segments using User Data Headers (UDH) so recipient devices can reassemble them correctly. These extra header data lower the payload to 153 characters for GSM-7 and 67 characters for Unicode per segment.

Alex Alabiso

Alex built Semaphore’s tech backbone and keeps it running smoothly. With deep experience in tech: Over 20 years in Web Development, IT and Infrastructure; 10+ years management experience in technology; and an expert in enterprise application architecture, development and tech processes, Alex is an old-hat in bridging the gap between geeks and suits as well as applying tech to real-world business problems. Connect with Alex on LinkedIn.

SMS may seem simple, but it remains one of the best ways to reach your customers. It’s direct, personal, and almost always read, usually within minutes. That’s why many businesses worldwide still rely on it to connect with customers.

But when your messages don’t get through, you may lose sales, confuse customers, and frustrate your staff. In most cases, these problems stem from just a few common causes that you can easily resolve.

This blog explains why SMS delivery fails and what you can do to keep your messages moving.

8 Common SMS Delivery Issues and Solutions

SMS delivery isn’t always plug-and-play. Behind every failed or delayed message is usually something technical or procedural that you can troubleshoot. Here are the most frequent culprits and what to do about them.

1. Invalid or inactive phone numbers

One of the most common reasons an SMS fails to deliver is that the recipient’s number is invalid or no longer active. This issue often occurs due to a lack of validation of customer data during sign-up or a lack of recent updates to the mobile user’s details.

To avoid this problem, you can run regular database cleanups and use real-time number validation tools that catch typos and inactive numbers before you send.

2. Carrier filtering or spam blocks

Mobile carriers automatically scan messages for spam-like content, like shortened URLs, suspicious sender names, or heavily promotional language.

That said, keep your content clear and concise to avoid spam triggers. Then, register your sender ID with local carriers so your customers know they’re receiving information directly from you.

Ideally, you work with a reputable provider, such as Semaphore. With a reliable SMS API and support for sender ID registration, we help your messages reach more people without the technical hassle.

3. Incorrect message formatting

If you forget to use E.164 number formatting (e.g., +639999123456), include a broken link, or insert unsupported characters, your message may never reach the recipient. Philippine carriers also have strict rules: no shortened URLs and no special characters that require Unicode encoding.

Use standard GSM (Global System for Mobile Communications) characters, adhere to the 160-character limit, and test your messages across devices. Plus, always send from a pre-registered sender name and avoid vague IDs like “SMS” or “TEST.”

A clean, correctly formatted message enhances SMS delivery and ensures compliance with regulations.

4. Poor network coverage

Even if everything is correct on your end, a poor signal on the recipient’s side can delay or block delivery. Phones that are turned off, roaming, or in low-coverage areas may not receive your message immediately.

The fix here is to configure retry logic or message expiration settings in your SMS platform so messages automatically resend when the device becomes reachable.

5. Outdated or misconfigured SMS gateway

If you’re using your SMS gateway or working with a low-tier provider, you may encounter issues with routing, encoding, or compatibility. Misconfigured gateways can silently block messages or cause failed handshakes with carriers, resulting in communication issues.

Partnering with a provider like Semaphore significantly reduces this risk. Our optimized infrastructure enables you to achieve speed, compliance, and high-volume delivery. This way, you can focus on your SMS marketing strategy while we handle the technical aspects of delivery.

6. Message length or character issues

If you exceed the 160-character limit, your SMS may be split into multiple messages or corrupted during transmission. Special characters and emojis can also switch the encoding from GSM to Unicode, reducing the maximum character count to 70 per message.

Use URL shorteners when necessary, limit emojis, and verify encoding in your SMS dashboard to ensure the SMS delivery is clean and error-free.

7. Lack of user opt-in or permissions

Sending texts to people without their permission creates legal risks and increases the chance of customers blocking or reporting your number. Some carriers filter traffic that they suspect comes from purchased or scraped lists.

To stay compliant and maintain good standing, build clear opt-in flows and honor opt-outs immediately. Use simple language, such as “Text YES to subscribe,” and always confirm when someone joins.

Make opting out just as easy. Include direct instructions, such as “Text STOP to unsubscribe,” and send a quick confirmation when someone opts out.

You can also offer alternatives, such as reducing message frequency instead of completely removing a subscriber. That way, you respect their preferences while keeping the door open for future engagement.

8. High-volume throttling or rate limits

Sending bulk messages haphazardly can trigger carrier limits or slow down the delivery process. If you repeatedly send hundreds of messages without receiving enough replies, carriers may flag your traffic as spam.

You may also encounter network overload during peak times, such as holidays or significant events. Your customers may not receive your messages on time or at all.

To avoid these issues, pace your sends. For large campaigns, consider spreading out your SMS or using multiple sender IDs to ensure a smooth process.

Get Your SMS Strategy Back on Track

Most SMS delivery problems aren’t mysterious—they are simply overlooked. The more you understand the rules behind delivery, formatting, and compliance, the better your results will be.

If you want an easier way to handle it all, consider Semaphore, a provider of trusted SMS marketing for businesses.

Our SMS API, bulk messaging tools, and real-time delivery tracking allow you to send thousands of promo alerts or customer updates. We’re here to help you succeed in the world of SMS marketing.

Explore our SMS solutions today and take control of your communication.