A Hestra size is the circumference of your hand in inches. Measure around the widest part of your palm, just below the knuckles, without the thumb. No measuring tape? Wrap a piece of string around your hand and measure it against a ruler.
Hand length is measured from the wrist to the tip of your middle finger.
Sport gloves stretch very little, so choose the right size from the start. A little air between your hand and the glove keeps you warm; a glove that is too tight feels cold. Between two sizes, go for the larger one.
The letter sizes are Hestra's own conversion. On unisex gloves the size button shows the men's letter, on women's models the women's. Junior gloves use a separate scale: a junior 7 is not an adult 7.
Sizes are a recommendation. Hands vary, and some models fit closer than others.