①Find the point between your eyebrows and hairline, right in the middle of your forehead ②Find the two points slightly above your ears ③Take a sewing measuring tape or soft tape measure (if you have no measuring tape, use a string and measure the resulting length with a ruler or yardstick). Wrap the measure around your head, passing points ① (about 0.5-1 inches above the eyebrows) and ② (slightly above the ears), and through the back of the head, which gives you the longest circumference. ④Measure your head several times to avoid mistakes and find the maximum circumference.
The best size for you to choose is: your head circumference +1 inch.