iPhone and Mac fonts problem

I try to use Helvetica font with size 13 pt. I have a problem, because I created an image with som开发者_JAVA百科e text with this font and font size. Added it to my iPhone project, then I created a UILabel, added top on this image which was created in photoshop, I've used the same font and font size and it's totally different. Why is that?

1 inch = 72 pt = 96 px, which means 9pt = 12px

In iOS, the font size is in pixels instead of points which might explain the difference.