如何计算在UILabel行中可以输入多少字符?

I want to make a UITableview with dynamic height for cell. In each cell i am displaying a message of varying text. Now i want that my table cell be according to the text of the message and also my label present on cell should display the text. I am making my table cell flexible on the basis of the number of characters that can accommodate in a line. But here is the problem. Different alphabets take different space. So, i am unable to calculate how many alphabets can come in a single line. Any Suggestions to this??? with dynamic heigh