A big challenge is to know "What size do I buy for myself or my child?"

Keeping in mind that this is a guideline.

I recommend using the "General" Sizing Chart and look at the size you normally wear.

Then take a look at the actual garment sizing chart and check the measurements against it. 

When measuring it is always best to use a clothing tape measure.

I would recommend leaning on the larger side if you fall at the top end of the chart.

This information is intended for use as a general guideline. Sizing and fit may vary somewhat by brand.  All measurements are in inches.