Please have a professional seamstress, or a gown/bridal store professionally take your measurements. VERY IMPORTANT
Bust - At the largest circumference.
Waist - Lean over to the side and measure at the bend. That would be your natural waistline.
Hips - Measure around the middle of your butt.
Remember - these dresses cannot be let out but can be brought in, so keep that in mind when ordering in case of alterations.