You could try a formula such as:
=SUMPRODUCT(--(LEN($AC$10:$AC$29)>0))
but that would take no account of hidden rows.
This might work though:
Code:
=SUMPRODUCT((LEN($AC$10:$AC$29)>0)*(SUBTOTAL(103,OFFSET($AC$10,ROW($AC$10:$AC$29)-MIN(ROW($AC$10:$AC$29)),0))))
yuk.