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 ( 38.6" ), waist ( 31.1" ), hips ( 43.3" ). Wearing size: 12 / L