To know the number of pages you are typing, look to the bottom left corner under the message box while typing. There you will see the number of page you are now, the number of characters you are typing and the total.
How Many Characters Makes a Page of Message?
The first page of message contains 160 characters, the second page takes 149 characters while the 3rd page and above takes 152 characters. Also note that a page of message to a phone number is charged at 1 unit while a two page message to a phone number is charged at 2 units and so on.
To see how this works exactly, do check out the short video tutorial below.