Are you saying you have a man's pattern rather than a Woman's cardigan?
If the pattern is plain stocking stitch you could probably do it with regard to the number of stitches per 10cm as on a tension square for the yarn you are using.
If it's a fancy pattern is concerned it's going to be a bit more complicated as you will need to have enough stitches to complete any pattern that involves a sequence of stitches.
Look at other woman's patterns your size to get an idea how many stitches you need for that garment. The important bit to get right is the width, ie number of stitches. The length of the body or sleeves as they are rows is much easier to adjust.