A text message on a mobile phone is 70 characters long. Why are Chinese full-width and English half-width characters both counted as 70 characters? It should be 140 characters in English!

The encoding used is different. Now the format of mobile phone text messages is generally PDU format. When it contains Chinese, the encoding is UCS2 (one word 16 bit). In pure English, the encoding uses 7-bits (one word is 7 bits).

The text message content is 140 bytes, and the Chinese full-width UCS2 encoding is (140 * 8)/16=70, while the English half-width Using 7-bits encoding, it should be (140 * 8)/7=160.