[plt-scheme] MrEd- precise font size

Given a particular font% object, is there any way to know what the exact
height and width of a string rendered in that font will be? Assume I use
the dc<%> draw-text method if that is relevant. Preferably
platform-independent but mostly interested in X11/Linux. I ask because I
want to build an application that lays out characters/string in a
grid-like fashion (like a spreadsheet) and I want to know how much space
each cell needs.
thanks,
Tato Norren