For a wig, use a soft tape around your head: start at your front hairline, go behind one ear, around your nape, behind the other ear and back to the front.
For a topper, measure the widest and longest part of the area you want to cover. Compare that with the base dimensions on the product page.
Sizes can vary by piece. If you’re between sizes or need help with shade, ask Nada about this piece before ordering.