To figure out your body measurements please do the following:
For bust; measure around the fullest part of your bust (wear a bra);
For waist; place the tape around your natural waist;
For hips; measure the fullest part usually 8" down from your waist:
For inseam; its easiest to measure pants you already have that are a good length for you - take the tape and measure down the inside seam from crotch to the hem. With your body measurement, check PGM Women Plus Size Table, select your suitable dress form.