You will want to measure her (bare-skinned) with a smooth tape measure and obtain the chest, waist and top of the shoulder to floor. Take the tape measure under her arms and go directly over the bust line. Get an actual measurement- do not place your finger or give an inch- you will want exactly what she is in inches. For the waist, you will want to go around her with the measuring tape right at the belly button. Some children have a slight pooch belly, so you will want to measure the widest point of where it sticks out. Most of our dresses should fall mid-calf to ankle so looking at the length measurement is important. You always have to consider the length measurements of the garment is from the top shoulder seam to the hem line- so that is where you will want to measure from. You will take the tape measure all the way down the front of her and see where it falls on the leg ...should be mid-calf to ankle for a ballerina length.