(5120 * 2880) / (3840 * 2160) = 1.77 Since they are both the same aspect ratio (16:9) you can also take the ratio of one linear dimension and square it to get

(5120 * 2880) / (3840 * 2160) = 1.77 Since they are both the same aspect ratio (16:9) you can also take the ratio of one linear dimension and square it to get the area ratio. So: (5120/3840)^2 = (2880/2160)^2 = 1.777