Most masks we sell are one size fits all. They are adjustable. The key measurement from the top of the mask to the bottom is almost always more than enough for most people. The extra space around your head is taken up with the adjustable or rubber straps.

_A general rule of thumb for our masks made by Respro is that they fit small. Our 3M Respirators run a little large with regard to the top and bottom measurement. With the 3M Respirators, it