When composing an SMS, don’t forget to keep track of your character count. All characters in an SMS count towards the length.
The science of Concatenation
You can send longer messages using a process called concatenation. Long messages are split into a series of smaller messages. We use special characters to join the long-format SMS together, and deliver them as one message. Due to the use of information to join the messages there are inconsistencies in the length of SMS characters.
This information is known as the user data header (UDH) and takes up 48 bits of each SMS payload, which means only 1072 bits are left over from the total max size of 1120 bits. This table illustrates the total number of characters available for your concatenated SMS message content, depending on the alphabet and character set used:
Special Characters and Different Languages
Languages such as Chinese and symbols like Emojis can be delivered by text message, but require extra information. This process reduces the text message size to allow for the extra information, which is measured in bits. Regular SMS messages have a maximum payload size of 1120 bits (140 octets or bytes). There are two types of character encoding, GSM and Unicode.
Latin-based languages such as English, French, and Spanish use GSM character encoding. Each GSM character accounts for 7 bits, thus allowing a maximum of 160 characters per SMS. Languages not supported by Latin-based languages use a different encoding process called Unicode. This is commonly known as Unicode Transformation Format (UTF-16).
Each UTF-16 character accounts for 16 bits per character, thus allowing a maximum of 70 characters per text. Depending on how many UTF-16 characters are used, this will make a noticeable affect on the final character count.
Lastly, don't forget that variables can affect your character count as well. For example when you use [First Name], calculate your count based off the longest first name in your list. Apply this to the rest of your variables as well.