A glove size chart for men's, women's, children's and unisex sizes is available at Glove.org. An additional chart for men and women that includes measurements in both inches and centimeters is available at LeatherGlovesOnline.com.
To find the correct glove size, take two measurements of the wearer's dominant hand. First, measure the circumference of the widest part of the palm, then measure the length from the tip of the longest finger to the base of the palm. The largest of the two measurements should be used to determine the appropriate glove size. Match the measurement to the letter size on the glove size chart.