For this tutorial I made for a child I used width of 3.5 inches for both front and back then for the depth I used 3.5inches for the front 1.5 for the back. This is not a constant figure individuals differs because of the different size of head circumference. Like I said in the tutorial u can make urs both front and back the same then you don’t need to add to the width standard measurements of 3inches will work for both the width and depth for both front and back for kids not adults.