Measure with a ruler around the bust/waist/hips and keep the ruler parallel to the ground.
Find the closest size to your bust/waist/hips circumference in the size table below (the bust/waist/hips circumference values in the table point to your figure size, not the size of the shapewear)
The measurements of the model in the picture: Bust ( 39.6″ ), waist ( 31.8″ ), hips ( 42.1″ ). Wearing size: 12 / XL