W pomocy do DrawText jest:
DT_CALCRECT Determines the width and height of the rectangle. If there are multiple lines of text, DrawText uses the width of the rectangle pointed to by the lpRect parameter and extends the base of the rectangle to bound the last line of text. If there is only one line of text, DrawText modifies the right side of the rectangle so that it bounds the last character in the line. In either case, DrawText returns the height of the formatted text but does not draw the text.
Return Values
If the function succeeds, the return value is the height of the text.
Czego więcej chcieć, tekst nie będzie szerszy niż to co jest podane w lpRect.
Jeżeli interesuje cie coś innego to radze spojrzeć na GetTextExtentPoint