Calculate a screen's width and height from its diagonal size and aspect ratio.
Calculator verified • Last updated: August 2026
—
The recomputed diagonal is a consistency check — it's calculated back from the width and height, and should match your entered diagonal almost exactly.
A screen's diagonal, width, and height form a right triangle, so the Pythagorean theorem connects them. Given the aspect ratio, the diagonal splits between width and height in proportion to the ratio numbers — each dimension gets the fraction of the diagonal equal to its own ratio number divided by the length of the ratio vector itself.
$$W = D \times \frac{R_w}{\sqrt{R_w^2 + R_h^2}} \qquad H = D \times \frac{R_h}{\sqrt{R_w^2 + R_h^2}}
D: diagonal screen size.
R_w, R_h: the two numbers of the aspect ratio (e.g. 16 and 9).
W, H: the calculated width and height, in the same unit as the diagonal.
A 24-inch screen at 16:9: the ratio vector's length is the square root of (16 squared plus 9 squared), or the square root of 337, about 18.36. Width is 24 times (16 divided by 18.36), about 20.92 inches; height is 24 times (9 divided by 18.36), about 11.77 inches. As a check, the square root of (20.92 squared plus 11.77 squared) comes back to almost exactly 24 inches — confirming the width and height are consistent with the original diagonal.
Two screens can share the exact same advertised diagonal size and still look and feel very different, because the aspect ratio changes how that diagonal length is distributed between width and height. A 24-inch 21:9 ultrawide monitor is noticeably wider but shorter than a 24-inch 16:9 monitor — useful for side-by-side windows, but with a smaller vertical viewing area and, in most cases, slightly less total screen area than the more square-ish 16:9 panel.
Assuming a screen's advertised diagonal alone tells you its width or height is a common mistake — the same diagonal number describes a different rectangle at every aspect ratio, so the ratio is essential information, not an optional detail.
Mixing up which ratio number corresponds to width versus height (entering a 9:16 portrait ratio when a 16:9 landscape ratio was intended) flips the calculated width and height entirely — always double-check that the wider number is entered as the ratio width for a landscape screen.
Diagonal Size — the distance measured corner to corner across the visible screen area; the number manufacturers use to advertise screen size.
Aspect Ratio — the proportional relationship between a screen's width and height, expressed as a simplified ratio like 16:9.
Ultrawide — a display with a wider-than-standard aspect ratio (commonly 21:9), offering extra horizontal space at the cost of vertical height compared to 16:9 at the same diagonal.
The diagonal, width, and height form a right triangle, so the Pythagorean theorem applies. Given the aspect ratio, the diagonal splits proportionally between width and height: width equals the diagonal times the ratio's width share, and height equals the diagonal times the ratio's height share, where each share is found by dividing that ratio number by the square root of the sum of both ratio numbers squared.
A single diagonal measurement gives one consistent number regardless of aspect ratio, making it easy to compare screens at a glance. Two screens with the same diagonal but different aspect ratios can have noticeably different width, height, and total area, which is why aspect ratio matters alongside the diagonal for understanding actual screen dimensions.
Not necessarily bigger in area — a wider ratio (like 21:9) at the same diagonal as a 16:9 screen is actually wider but shorter, and typically has slightly less total screen area than a 16:9 screen of the same diagonal, since a more square-ish shape maximizes area for a given diagonal.