What is SMS credit? How many letters can I write in a SMS?

SMS stands for Short Message Service and is also commonly referred to as a “text message”. With a SMS, you can send a message of up to 160 characters to another device or another mobile phone.
1 SMS Credit = 160 characters including spaces in English.
In newly added *Promotional Route, you can send a message with the length of 360 characters through a single message, but your SMS credits will deducted as per Letters used in the message.
The message length allowed for 1 credit message is 160 characters. If the text length exceeds 160 characters, then the message consumes 2 credits. The character length for 2 messages is 306.
The calculations are as below:
ENGLISH SMS credits - Counting Mechanism
160 letters = 1 SMS credit
160+146 = 306 letters = 2 SMS credits