This might get you close.

Width = width in pixels.
NumberOfCharactersPerLine = FLOOR(m.Width / FONTMETRIC(6, m.FontName, m.FontSize, m.FontStyle))
SET MEMOWIDTH TO m.NumberOfCharactersPerLine
RETURN MEMLINES(m.Text) * FONTMETRIC(1, m.FontName, m.FontSize, m.FontStyle)

>How I know the number lines in a report, from a memo field with asimetric font.
>
>This before printing.
>with simetric font i dont have problem.
>I can calculate using set memowidth and memlines.