SMS character limits, Unicode and message length

How many characters is one SMS?

160, if every character is in the GSM-7 alphabet. If the message contains even one character outside that alphabet, the whole message switches to Unicode encoding and the limit drops to 70 characters. This is a property of the SMS standard, not of any particular provider.

The reason is bit width. An SMS payload is 140 bytes. GSM-7 packs each character into 7 bits, so 140 bytes hold 160 characters. Unicode (UCS-2) uses 16 bits per character, so the same 140 bytes hold only 70. There is no middle setting: one out-of-alphabet character converts the entire message.

What is in the GSM-7 alphabet?

• A to Z and a to z, and the digits 0 to 9.
• Common punctuation: . , ? ! : ; ' " ( ) / + - * # % & @ _
• A handful of accented and Greek letters, and the currency symbols $ and the euro sign.
• Space, carriage return and line feed.

Two extra GSM-7 characters count double: characters in the extension table, notably the square and curly brackets, the backslash, the tilde, the caret and the vertical bar. Each of those consumes two of your 160.

Long messages: concatenation

A message longer than one SMS is split into parts and sent separately, each carrying a small header telling the handset how to reassemble them. The header consumes payload, so a linked part holds 153 GSM-7 characters instead of 160, or 67 Unicode characters instead of 70.

The recipient normally sees one message: reassembly happens on the handset. What they do not see is that you paid for every part. This is also why a message that lands at 161 characters is the most expensive edit in messaging - one character doubles the price.

Hausa, Igbo, Yoruba and Nigerian Pidgin

Plain Nigerian Pidgin written in unaccented Latin letters stays in GSM-7 and keeps the full 160 characters. Hausa, Igbo and Yoruba written properly do not: their orthographies use characters outside the GSM-7 alphabet, so any correctly written message drops to the Unicode limit.

How Sendozi counts and bills

Sendozi bills ₦7.00 per page, and a page is one message on the network, so the alphabet sets the page size: 160 characters in GSM-7, 70 in Unicode. Going past the first page splits the message, and every part - including the first - then gives up room to the header that reassembles it, which is why two pages hold 306 characters rather than 320. A single send cannot exceed seven pages: 1000 characters in GSM-7, 469 in Unicode.

The practical guidance follows from that: watch the encoding, not only the character count, keep transactional messages inside one page, and preview the page count before a campaign. The dashboard shows the encoding and the pages as you type, and the pricing guide works through costed examples.

Writing to fit

• Drop the greeting. "Hi Chidi," is nine characters that carry no information the message body lacks.
• Use a link shortener for URLs, but keep the domain recognisable - an unfamiliar shortener in a bank alert reads as phishing.
• Write numerals, not words: 10, not ten.
• Cut the closing signature. The sender ID already says who you are.
• Replace smart punctuation with straight equivalents before sending.
• Test the longest possible merge-field expansion, not the average one. A long name is what pushes a template over the boundary.