Understanding SMS Character Limits and How They Affect Messaging

Introduction

When sending SMS messages, it’s important to understand character limits and how they impact message delivery. SMS (Short Message Service) uses specific encoding methods that determine the number of characters that can be sent in a single message. Exceeding these limits can cause messages to be split into multiple parts, increasing costs and affecting readability.

This article explains SMS character limits, encoding types, and best practices for managing message length.

SMS Character Limits & Encoding Types

SMS messages are encoded using either GSM-7 or Unicode (UCS-2), which determines the number of characters that fit in a single SMS.

1. GSM-7 Encoding (Standard Characters)

• Character Limit: 160 characters per SMS
• Supported Characters: Basic Latin characters, numbers, and common symbols.
• Concatenated Messages: If a message exceeds 160 characters, it is split into multiple parts. Each part is limited to 153 characters to accommodate linking metadata.

? Example:

• "Hello! This is a standard SMS message." (✅ Fits in 1 message)
• "This message is longer than 160 characters, so it will be split into multiple parts, meaning it will cost more to send." (❌ Split into multiple messages)

2. Unicode (UCS-2) Encoding (Special Characters & Emojis)

• Character Limit: 70 characters per SMS
• Used For: Messages containing special symbols, non-Latin characters (e.g., Chinese, Arabic, Cyrillic), or emojis.
• Concatenated Messages: If a message exceeds 70 characters, it is split into multiple parts, with each part limited to 67 characters due to metadata.

? Example:

• "Hello! ?" (✅ 1 message, as emoji triggers Unicode)
• "This message contains an emoji ? and is longer than 70 characters, so it will be split into multiple parts." (❌ Split into multiple messages)

How Multi-Part SMS Works

When a message exceeds the character limit, it is sent as multiple SMS parts and reassembled on the recipient’s device. However, each part is billed as a separate message.

? GSM-7: Messages over 160 characters are split into 153-character segments.
? Unicode: Messages over 70 characters are split into 67-character segments.

? Example of a Split Message Using GSM-7:

• "This is a message that is over 160 characters long, so it will be split into multiple parts. The system will link the parts together so the recipient sees it as one message, but each part counts towards the total SMS cost."
• Total characters: 211
• Sent as: 2 messages (153 + 58 characters)

How to Optimise SMS Messages & Reduce Costs

1. Keep messages concise – Stay within 160 characters for GSM-7 and 70 characters for Unicode to avoid multi-part messages.
2. Avoid unnecessary special characters – Emojis, symbols, and non-Latin scripts trigger Unicode encoding, reducing the character limit.
3. Use abbreviations where appropriate – As long as they are understandable.
4. Consider using a URL shortener – If including links, shortening them can save character space.
5. Check message length before sending – Some SMS platforms display the character count and estimated number of SMS parts.