Take a look at the illustration in the FAQ sticky thread.
How big your font looks at 12 point compared to Arial or other standard fonts depends on the x-height, caps height, and how much space is left above and below the glyph contours for accents. The entire design should always be constrained within the WinAscent and WinDescent lines, which can be recalculated in Font Properties, Metrics, Maximum, Calculate. Just doing that may increase the apparent size of your font in Windows applications.