px is a measure of length, not area. A 12 px high font is 24 px high on a retina display. A 12 px by 12 px box is 144 px^2, or 12 x 12 x 2 x 2 = 576 px^2 on r

px is a measure of length, not area. A 12 px high font is 24 px high on a retina display. A 12 px by 12 px box is 144 px^2, or 12 x 12 x 2 x 2 = 576 px^2 on retina.