Size & Fit Recommendations
A snug, tight fit is preferred by most ball players. The 9 STRAP sizes will typically coincide with your batting glove size. If you do not wear batting gloves, you may want to size down for more comfort and effectiveness.
Right-handed batters will place the 9 STRAP on their right hand. Left handed batters will place the 9 STRAP on their left hand.
Sizing Video (you can also read alt. text below)
How to measure your hand:
Find a tailor's tape or a flexible sewing tape measure. Now, use this to measure the circumference of your hand. You'll want to measure the area of your hand where the 9 Strap would be placed. Do not cinch the tape measure tightly. Likewise, do not measure it loosely. Measure it comfortably, and be sure to extend the thumb in order to get a proper measurement for your 9 Strap.
Note: if you do not have access to a tailor's tape measure, you can use a piece of ribbon or strip of paper, and follow these same instructions and then measure the strip with a flat ruler or tape measure.
Size Chart
Now use the attached chart to determine your size.
If your hand measures at 7.25", and you do wear batting gloves, then you'd want to purchase a Youth Small. If you do not wear batting gloves, then you'd want to size down to a Youth XS.
Likewise, if your hand measures at 9", then you'd want to purchase an Adult Large 9 Strap to fit over your batting glove. However, if you do not wear batting gloves, or your batting gloves allow you to wear your 9 Strap on your bare hand and have the strap fit through the slit in the side of the glove, then you'd want to purchase an Adult Medium 9 Strap.