Check out Emmett Rhyse's Review:
Jockmail underwear runs small. Do NOT order your "normal" size underwear. We also don't recommend ordering your regular jeans size. Jockmail is low rise and sits on your hips and not your true waist. Instead, measure the part of your waist where your underwear band rests and consult the guide below for correct sizing. If you have bigger thighs, we recommend choosing the jockstrap or brief models as the legs can also be a bit tight.
MEDIUM - 27-29"
LARGE - 30-32"
EXTRA LARGE - 33-35"
XXL - 36-38"
Wash in cold water. Drying this product in the dryer will result in normal cotton shrinkage. If you'd like to minimize this, your Jockmail underwear can be air-dried.