Use a soft measuring tape
Wrap the tape around your head about 1/8 inch above your eyebrows
Keep the tape level all the way around
Measure over the fullest part of the back of your head
Make sure the tape is snug, not tight
Read the measurement in inches or centimeters
Measure twice to confirm accuracy
Compare the measurement to the hat brand’s size chart
If between sizes, choose the larger size
Try the hat on if possible to check fit