I have used TextRenderer to Measure the length of a string and therefore size a control appropriately. Is there an equivalent in WPF or can I simply use T
Take a look at the FormattedText class
If you need more granular control, then you'd need to descend to the GlyphTypeface type's AdvanceWidths member. Found a similar discussion here with a code snippet that looks like it might work.
Update: Looks like this may be a duplicate of Measuring text in WPF .. OP please confirm.