With GetHeight, you would not need to specify width...
Oh, sorry I don't know how to handle RichCell and RichText properly
To create that test cell we would still need to know the correct width right?
If you put nothing into it, just empty paragraph with proper font set, it will give you the height you need.
(Although, this might not be guaranteed in the future. Today, single line / single font cell height only depends on the font set. It is possible that with advanced unicode support, we will need to adjust that for characters with multiple marking that will extend the height of individual characters...)