The industry consider true plus size to be sizes above a UK size 18. One of the most important things we will consider for grading plus size is what type of body shape will the clients be as there is much greater variety in plus size bodies. There are also many opportunities for expansion in this market sector as different lines can target more niche body shapes such as plus size tall garments.
If you are planning to extend a previously established line above this threshold we would recommend creating an additional base size pattern in order to account for the different allowances needed in various parts of the garment. For example special attention needs to be paid to the measurements of the armhole, shoulder length, across back, bust waist and hips ratio.
If you are starting a new line devoted just to plus size clothing and need advice on standard grade rules for plus size we would recommend creating a base size pattern in sizes 18 or 22.