Our masks are offered in two standard sizes. For purposes of ordering, those two sizes will be referred to as Men's (or Large) and Women's (or Medium). To determine the correct sizes required, use a fabric measuring tape and measure from just in front of each ear lobe across the bridge of the nose (the middle part; not the top of the nose, not the tip of the nose). We usually find that this measurement in men will be 12 inches and for women it is 11 inches. Bear that in mind when specifying your size, as it may not necessarily correspond to your gender.