Summarize the following:
Use a cloth tape measure to measure along the hairline. The tape measure should extend from the base of your hairline at your neck to the top of your hairline at the forehead.  The tape measure should wrap just above the ears on either side of your head. Do not pull the tape measure. It should lie flat against flattened hair, but it should not be taut. Place the end of a cloth tape measure at the center of your forehead, matching the end of the tape measure to the beginning of your natural hairline. Drape the tape measure over the crown of your head and down to the middle of the nape, where you natural hairline ends. As before, do not pull the tape measure. It should lie flat against flattened hair without being taut. Bring the end of the cloth tape measure to the uppermost point at which your ear connects to the rest of your head. Drape the tape measure over the crown of your head and back down to the same position of the opposite ear.  The tape measure should rest on both ears along the point at which eyeglasses or sunglasses would sit. Once again, the tape measure should lie flat against flattened hair but should not be pulled tight.

Summary:
Measure around the head at the hairline. Measure down the center top of your head. Measure from one ear to the other.