This can't be said to be a certain number. For example, everyone's waistline and bust are different, the thickness of sweater needles, the choice of wool are different, and the number of needles needed is different. You can start 10 stitch with the prepared sweater needle and sweater thread, and then knit for a certain distance. Then according to the width of the weave, combined with the width of this person's clothes, you will have a general concept.