You can look at or measure your old pair of glasses to get the dimension which fits you the best. By having these numbers, you can easily find the closest match in our website. Eye Size - refers to the horizontal width in millimeters of one of the frame's lenses.Bridge Size - measurement is the distance in millimeters between the two lenses. It is measured between the two closest points of the two lenses.Temple Size - is measured along the length of the temple, from one end to the other, including the bend.Vertical Size (B) - refers to the vertical height of an eyeglasses lens, and is measured from the tip to the bottom of the lens aperture of the frame. The measurements are taken from a horizontal line intersecting with the top of the lens, to the horizontal line intersecting with the bottom edge of the lens. The B measurement is only important when ordering multifocal lenses; follow this link to read more about progressive lenses.