Take the total length of the dress from the size chart in the pattern and subtract the desired total tunic length. For example, the Size and Measurement Chart in the pattern says that the size 5 dress is 23.5”, from shoulder to hem, finished. The desired tunic length is 18
23.5” (finished dress length) – 18” (desired tunic length) = 5.5”
So, for a size 5, the tunic needs to be 5.5 inches shorter. If you are creating the double tier ruffle skirt you will subtract the 5.5 inches from the length of the tier 1 skirt piece. The tier 1 ruffle, tier2 skirt and tier 2 ruffle pieces will remain the same as they are in the pattern. If making the single ruffle hem skirt you will subtract the length from the skirt.
Don't forget to upload a picture of your progress into the Lahaina SewAlong album in the Little Lizard King Facebook Sewing Group!