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Short Message Service (SMS)

Short Message Service is a standard protocol that lets devices send and receive text messages. It was designed to use the spaces between other signals, which explains why messages are limited to 160 characters (using 7-bit encoding), or 140 bytes. SMS was first standardized in 1985 as part of GSM, and later built into the SMPP protocol that carries SMS messages.

What’s a Segment in a text message?

A single SMS message technically supports up to 160 characters, or up to 70 if the message contains one or more Unicode characters (such as emoji or Chinese characters).

If your messages exceed 160 characters, additional credits/SMS will be used or counted. Larger text messages are split into 153-character "segments" and sent individually, then re-assembled by the client's (recipient's) device.

SMS are billed for every message segment sent. If, for example, you send a message that is 140 characters long, you will be charged for one segment. If you send a message containing more than 160 characters to the same phone number, say 170 characters, your text message will now cost 2 segments.

Note: Keep messages under 320 characters for best deliverability.

Note: Some messaging platforms may only support messages up to 1600 characters.

SMS message length and character encoding

When SMS messages include non-GSM-7 characters (like Chinese script or emoji), they must use UCS-2 encoding. These messages can contain a maximum of 70 characters in a single, non-segmented message. If your UCS-2 message exceeds 70 characters, it will automatically split into multiple 67-character segments.

GSM-7 encoded messages

• 0-160 Characters: 1 segment
• 161-306 Characters: 2 segments
• 307-459 Characters: 3 segments

• And so on...

UCS-2 encoded messages

• 0-70 Characters: 1 segment
• 71-141 Characters: 2 segments
• 141-212 Characters: 3 segments

• And so on...

GSM-7 characters

A text message containing regular letters and numbers will be encoded using GSM-7.

GSM-7 example:

@ £ $ ¥ è é ù ì ò Ç Ø ø Å å Δ _ Φ Γ Λ Ω Π Ψ Σ Θ Ξ ESC Æ æ ß É ! " # ¤ % & ' ( ) * + , - . / 0 1 2 3 4 5 6 7 8 9 : ; < = > ? ¡ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Ä Ö Ñ Ü § ¿ a b c d e f g h i j k l m n o p q r s t u v w x y z ä ö ñ ü à

Unicode characters

A text message containing emojis or special characters like the Chinese script will be encoded using UCS-2 (known as Unicode characters). Even just one unicode character will change the encoding of your SMS.

Emoji unicode example:

😀 😁 😂 🤣 😃 👌

Non-emoji unicode example:

¢ ¦ ¨ © ª « ¬ ® ¯ ° ± ¹ ² ³ ´ µ ¶ · ¸ ¹ º » ¼ ½ ¾ À Á Â Ã È Ê Ë Ì Í Î Ï Ð Ò Ó Ô Õ × Ù Ú Û Ý Þ á â ã ç ê ë í î ï ð ó ô õ ÷ ú û ý þ ÿ