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 ( 41.7" ), waist ( 33.9" ), hips ( 47.2" ). Wearing size: 14 / L