Problem with spacing

i have a strip of buttons made in a for loop :

this.createTextField(["btn"+i], this.getNextHighestDepth(), m, 5, 0, 0);
 this.createEmptyMovieClip(["BtnClip"+i], this.getNextHighestDepth());

the textFields text comes from an Array and has a diffrent length of text.
the m that i have in the first line represents the x location of each textField so i used this:

m = m+this["btn"+i].length*7;

my problem is that the spaces are not equal and i need to know if there is a way to know the length of the textField not by letters because it looks like using the number of charcters is not accurate?