To properly fit the glove dry, you should have to really wiggle your hand into it. To “fit like a glove” It must be snug because it will stretch when wet. It is OK to be tight, because an oversized waterski or wakeboarding glove will fold in your palm and create blisters.
Glove Sizing Chart
Print out this page and place your right hand as shown, with your index finger against the black line. The measurement that follows the right side of your hand is your approximate glove size.
You can more accurately measure your glove size by using a tape measure as shown below. Wrap a tape measure around your hand at the widest point (usually the knuckles) and make a loose fist. Note that measurement, round to the nearest .25″ (0.1 cm) and refer to the chart below to find your approximate glove size.