Chest: Holding a tape measure horizontally, measure your waist circumference at the narrowest point, i.e. where your torso tilts when you bend to the side.
Waist: Standing straight with your feet together, hold the tape horizontally, and measure the circumference of your hips at the widest point.
Inside leg: Holding the tape vertically, measure the distance from your groin to your ankle.
N.B.: the garment you receive may have EU sizing on the external label, as Diadora is an Italian brand. During the purchase phase, simply select your size; it will already be converted for your country of residence (US). If you are not satisfied with the fit, remember that returns are free.