---
title: "GSM-7 encoding"
description: "GSM-7 is the default 7-bit SMS alphabet defined in 3GPP TS 23.038 (formerly GSM 03.38). It fits 160 characters in a single SMS, or 153 per segment when a message is split."
canonical: "https://omnichannels.ai/glossary/gsm-7/"
language: "en"
updated: "2026-10-10"
publisher: "BroadNet Technologies"
brand: "OmniChannels.ai"
---

# GSM-7 encoding

Canonical: https://omnichannels.ai/glossary/gsm-7/
Language: en
Publisher: OmniChannels.ai by BroadNet Technologies

**Definition:** GSM-7 is the default 7-bit SMS alphabet defined in 3GPP TS 23.038 (formerly GSM 03.38). It fits 160 characters in a single SMS, or 153 per segment when a message is split.

An SMS carries up to 140 octets of user data (3GPP TS 23.040). Packing 7-bit characters gives 140 × 8 / 7 = 160 characters. GSM-7 covers basic Latin letters, digits, common punctuation and some accented and Greek letters.

Some characters live in an extension table reached through an escape character, so each counts as two: the form feed and ^ { } \ [ ] ~ | €. A message with a few euro signs or braces therefore holds fewer than 160 visible characters.

If any character in the message is outside GSM-7 and its extension table — an Arabic letter, an emoji, or a curly quote pasted from a word processor — the whole message switches to UCS-2, which fits only 70 characters per SMS.

For long messages, a user data header takes space in every segment, leaving 153 GSM-7 characters per part (152 with a 16-bit reference number). An escaped character is never split across two segments.

Check messages before a campaign: replacing one smart quote with a straight quote can halve the number of billed segments.

## Example

```
"Your code is 123456" = 19 GSM-7 characters, 1 segment. "Price: 20€" = 10 characters but 11 septets, because € is sent as escape + code.
```

## Sources

- [3GPP TS 23.038 — Alphabets and language-specific information](https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=745)
- [3GPP TS 23.040 — Technical realization of the Short Message Service (SMS)](https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=747)