A single text message looks simple until the bill arrives and one campaign of 5,000 messages was actually billed as 10,000. This usually comes down to one thing: character limits. SMS has strict rules about how many characters fit in a message, and those rules change depending on the characters you use.
Most businesses discover this the hard way, after a template with a curly apostrophe or an emoji quietly doubles the cost of every reminder sent that month. The rules themselves are not complicated, but they are easy to overlook when writing message templates quickly.
This guide explains exactly how SMS character limits work in Australia, the difference between standard GSM-7 and Unicode encoding, and how long messages get split into multiple billable segments. By the end, you will know how to write messages that stay within a single segment, avoid accidental Unicode charges, and keep your SMS costs predictable.
What Is an SMS Character Limit?
An SMS character limit is the maximum number of characters that fit into a single SMS segment before the message is split into multiple parts for delivery. A standard SMS using GSM-7 encoding holds up to 160 characters. If a message uses characters outside the GSM-7 alphabet, such as emojis, curly quotes, or certain accented letters, it switches to Unicode (UCS-2) encoding, which lowers the limit to 70 characters.
When a message exceeds this single-segment limit, it is not rejected. Instead, it is broken into multiple linked segments and reassembled on the recipient's phone as one message. Each segment carries fewer characters than a standalone message, 153 for GSM-7 or 67 for Unicode, because part of each segment is used for the header that tells the phone how to reassemble the parts. Carriers and SMS providers bill per segment, so a 300-character message can be charged as two or three messages depending on encoding.
Why It Matters for Australian Businesses
For Australian businesses sending SMS at scale, character limits directly affect cost and deliverability. A booking confirmation, delivery update, or marketing offer that unintentionally crosses into a second or third segment is billed at two or three times the price, even if the sender never intended to send a long message.
This matters most for businesses sending high volumes, such as clinics sending appointment reminders, retailers running SMS campaigns, or SaaS platforms sending OTP codes. A small formatting habit, like copying text from Word with smart quotes, can silently push every message into Unicode encoding and double the segment count across an entire contact list.
Understanding character limits before a campaign goes out protects the budget and keeps message delivery predictable. It also matters for compliance and customer trust: messages that arrive split across multiple texts, sometimes out of order on older handsets, look unprofessional compared to a single clean message. For time-sensitive alerts like OTP codes or appointment reminders, a predictable single-segment format also reduces the chance of delayed delivery during high traffic periods.
Key Benefits of Understanding SMS Character Limits
Cost control: Knowing the exact character count per segment means you can budget SMS campaigns accurately instead of being surprised by multi-segment billing.
Better deliverability: Shorter, single-segment messages tend to arrive faster and display more reliably across different phone models and carriers.
Cleaner customer experience: Messages that stay within one segment avoid awkward splitting on older devices, where multi-part messages can occasionally arrive out of order.
Smarter copywriting: Writing to a 160-character limit forces clear, direct messaging, which tends to perform better for reminders and marketing than long paragraphs.
Fewer encoding surprises: Understanding what triggers Unicode encoding helps you avoid accidental cost increases from emojis or special characters used without a clear reason.
How SMS Character Limits Work: A Step-by-Step Guide
Here is how SMS character limits work in practice, and how to plan messages around them.
1. Understand GSM-7 encoding
GSM-7 is the standard SMS alphabet and covers the basic Latin alphabet, numbers, and common punctuation such as periods, commas, and standard straight quotes. A single GSM-7 message holds 160 characters. If your message uses only these characters and stays under 160, it sends as one segment.
2. Know what triggers Unicode encoding
Unicode (UCS-2) encoding is used the moment a message contains a character outside the GSM-7 set. Common triggers include emojis, curly or smart quotes (“ ” instead of straight quotes), em dashes, accented characters like é or ü, and non-Latin scripts. Once Unicode is triggered, the limit drops to 70 characters for the entire message, not just the special character.
3. Calculate segments for longer messages
When a message exceeds the single-segment limit, it is split into concatenated segments. GSM-7 concatenated segments hold 153 characters each (not 160), because 7 characters are reserved for the reassembly header. Unicode concatenated segments hold 67 characters each instead of 70. A 200-character GSM-7 message, for example, sends as two segments: one segment covering the first 153 characters and a second covering the remaining 47.
4. Watch for hidden Unicode characters
The most common accidental Unicode trigger is copying text from word processors or design tools, which often auto-convert straight quotes and hyphens into curly quotes and em dashes. Always check message templates in plain text before sending, especially for automated reminders and campaigns that reuse a saved template.
5. Test before sending at volume
Before launching a bulk campaign, send a test message to yourself and check the character count against your platform's segment calculator. This confirms the encoding type and segment count match your expectations before the message goes to your full contact list.
6. Plan for links and personalisation
Personalisation fields like {first_name} and tracking links add characters that are easy to underestimate. Always calculate the character count using the longest possible value for each variable field, not the average, so a long name or full URL does not push the message into a second segment unexpectedly.
Common Scenarios and Segment Counts
A few real-world examples make the segment rules easier to apply.
A 155-character appointment reminder with no special characters: Sends as one GSM-7 segment. Billed as a single message.
The same reminder with a single thumbs-up emoji added: Switches to Unicode. Because it now exceeds 70 characters, it splits into three segments instead of one.
A 320-character marketing message in plain GSM-7 text: Splits into three concatenated segments of 153 characters each, since it exceeds the 160-character single-segment limit.
A template pasted from a Word document with curly quotes: Every straight quote becomes a curly quote, forcing Unicode encoding across the entire message even though no emoji was used.
How DataFlows Helps
DataFlows handles character counting and encoding detection automatically across its SMS API, Bulk SMS, and SMS Campaigns products, so you always know how many segments a message will use before it sends.
When sending through the SMS API, each request returns the calculated segment count and encoding type, letting your application flag long or Unicode-heavy messages before they go out. This is useful for OTP Verification messages and transactional alerts, where consistent, predictable formatting matters and delays can affect the user experience.
For teams sending through SMS Campaigns and Contact Lists, the message composer shows a live character counter and segment estimate as you type, so you can adjust wording before scheduling a send to your full audience. This makes it easy to catch a stray emoji or curly quote before a campaign goes out to thousands of contacts rather than after the invoice arrives.
SMS Automation workflows, such as appointment reminders or order updates, use the same encoding detection to keep recurring messages within a single segment wherever possible. Virtual Numbers and Sender IDs used for these sends are unaffected by character encoding, but the message body itself still follows the same GSM-7 and Unicode rules described above.
If you are integrating directly with the API, head to the Developer section in your DataFlows dashboard to get your API Token, then use it to test message payloads and review the segment count returned in the API response before sending live traffic.
Best Practices for Managing SMS Character Limits
Write to 160 characters: Aim to keep standard messages under 160 characters so they send as a single GSM-7 segment and avoid extra charges.
Avoid smart quotes and em dashes: Use straight quotes (" ') and standard hyphens (-) instead of curly quotes and em dashes, which silently switch the whole message to Unicode.
Use emojis sparingly: A single emoji forces Unicode encoding and drops your limit from 160 to 70 characters, so reserve emojis for messages where the impact justifies the cost.
Check personalisation field lengths: Test merge fields like names and order numbers with their longest realistic value, not a short example, before calculating segment count.
Shorten links: Use a link shortener for URLs in SMS Marketing and SMS Campaigns messages to reduce character count and leave more room for your message.
Review sending reports regularly: Check delivery and segment reports after each campaign to spot templates that are consistently sending as multiple segments, then revise the wording.
Conclusion
SMS character limits are simple once you know the rules: 160 characters for standard GSM-7 messages, 70 for Unicode, and reduced segment sizes of 153 and 67 characters once a message is split into multiple parts. Getting this right keeps your SMS costs predictable and your messages arriving cleanly, whether you are sending a handful of reminders a day or a bulk campaign to thousands of contacts.
Sign up at dataflows.com.au to start sending SMS with automatic segment and encoding visibility built in.
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