textfield get width of text?

I'm aligning a plugin to the left of a textfield which is aligned right..
Without setting a width, default width is like 400px. I can get the text length and try to calculate "fit" but depending on the number of characters used, the actual width of the typography may exceed my calculation or create much more width than necessary.
So how do I set the width of the textfield accurately?
autosize works great for height.. but is this issue why width was not supported?