Here's an old post of mine. This is mitten measurements. For gloves, you will take the distance from the cuff to the thumb and add 2 inches. For the medium size, this will be about 4 1/2 inches.
Looking at this post, I'm not seeing the circumference around the hand. This chart from Knitting on the Net is pretty accurate. These measurements will also work for crocheted mittens and gloves. I just made mittens for my one year old granddaughter using this chart and they fit.