SMS character limits
The short answer is 306 characters.
However, not all characters are counted the same way. Depending on the characters used in your message, some may count as multiple characters toward the limit.
Workshop automatically sends SMS messages using the most compact encoding available to maximize the amount of content that can fit within a message.
How SMS character encoding works
SMS uses a standard character set called GSM-7. When your message contains only GSM-7 characters, each character generally counts as a single character toward the 306-character limit.
If your message contains unsupported characters, such as emojis, the message may be encoded using UTF-16, which increases the number of characters consumed and reduces the amount of text that can fit within a message.
GSM-7
If your text message contains no special characters/only GSM-7 safe characters, each character will count as 1 character toward the 306 limit. These characters include:
- Numbers: 0-9
- Uppercase letters: A-Z
- Lowercase letters: a-z
- Symbols & punctuation: " # $ % & ' ( ) * + , - . / : ; < = > ? @ [ \ \ ] ^ _ { } | ~ \n \r !\
- Special characters: £ ¥ è é ù ì ò Ø ø Å å Æ æ ß É ¡ Ä Ö Ñ Ü ¿ ä ö ñ ü à
Non GSM-7, replaceable characters
Some characters are not GSM-7 compatible but can be safely converted to GSM-7 alternatives.
When these characters are detected, Workshop automatically replaces them before sending.
This helps preserve message length and ensures broad carrier compatibility.
An example of this type of character is ¼ and it will be replaced with 1/4
Non GSM-7, non-replaceable characters
Some characters cannot be converted to GSM-7 equivalents.
Common examples include:
- Emojis 😀 🎉 👍
- Certain special symbols
- Characters from non-Latin alphabets
When these characters are present, the message is encoded using UTF-16.
In UTF-16, characters can consume 2–5 characters toward your SMS limit, significantly reducing the amount of content that can fit within a message.
How merge tags affect character counts
Merge tags count toward the SMS character limit based on the value that is inserted for each recipient.
For example:
Message template:
Hi {{first_name}}, please complete your onboarding tasks.
If the recipient's first name is:
- Sam → 3 characters are added to the message
- Alexandra → 9 characters are added to the message
Because merge tags are replaced with real employee data at send time, the final SMS length can vary from recipient to recipient.
Why merge tag values are limited to 30 characters
Workshop limits merge tag values used in SMS messages to 30 characters.
This limit helps ensure:
- Messages remain within SMS character limits
- Personalized content does not unexpectedly increase message length
- SMS segmentation and delivery costs remain predictable
- Recipients receive a consistent messaging experience
Without a limit, unusually long employee attributes (such as job titles, department names, or custom fields) could significantly increase message length and cause messages to exceed the intended SMS size.
For SMS communications, we recommend using merge tags with concise attributes such as:
- First name
- Last name
- Preferred name
- Office location
- Department