Createtextfile: dimension file

Hi, I am using the formula CreateTextFile to create a file.txt in which I have to put a precisely number of characters and I did it completing the field with rpad formuala. In the file I must have 500 characters that should corrispond to a file of 500kb 1kb for each characters but my file is always larger then that like 700kb. 

Can someone help me ? I have already test if the number of characters and spaces are correct even using a online program to count them and they are 500 but if i put them into the text on the file,  it will be 700kb. 

Thanks!