XPLMGetFontDimensions
XPLM_API void XPLMGetFontDimensions(
XPLMFontID inFontID,
int * outCharWidth, /* Can be NULL */
int * outCharHeight, /* Can be NULL */
int * outDigitsOnly); /* Can be NULL */
This routine returns the width and height of a character in a given font. It also tells you if the font only supports numeric digits. Pass NULL if you don’t need a given field. Note that for a proportional font the width will be an arbitrary, hopefully average width.