Canvas content size

[SushiZZ]

I'm writing text into a canvas (using it as part of a terminal solution, so with a terminal font) but can't seem to find a consistantly accurate way of calculating the screen size to readjust the canvas size to the content. Am I missing something that would automatically snap the canvas size to the content size or maybe a maximum width/height used in the canvas? Alternatively, has anyone a suggestion as to how to accurately calculate the required width/height based on the font size?