Measure the chest at the widest part of the ribcage (usually just under the armpits), the waist at the smallest part between the ribcage and hips, and the hips at the widest part around the hips/bum area. The torso is measured by holding one end of a tape measure to one shoulder, and looping the tape measure down the chest through the crotch and up the back to meet at the same shoulder.
Always measure either over a leotard, or the underwear that will be worn under a leotard.
Tick Tock Designs leotards are designed to fit like a second skin. For a competition leotard, order the size that best matches your measurements. For training leotards, and/or if you need growing room, please size up.