Screen Ratio Calculator

A screen ratio compares a display's width to its height and throws the size away. A 1920 x 1080 laptop and an 85-inch 3840 x 2160 television are both 16:9, because the two numbers share the same proportion even though one has sixteen times the pixels of the other. The ratio is the shape; the pixel count is how much detail that shape holds.

1920 x 1080 becomes 16:9 because both numbers divide by 120. 1920 / 120 = 16 and 1080 / 120 = 9. That divisor — the greatest common divisor — is the whole reason ratios get written as small numbers: 1920:1080, 192:108 and 16:9 are the same rectangle, and 16:9 is the version people actually say out loud.

Ratio is not resolution, and the two are mixed up constantly when people shop for a display. Resolution is the pixel grid (1920 x 1080); ratio is the proportion of that grid (16:9). Two phones can share a 19.5:9 screen ratio while one ships at 1080 x 2340 and the other at 1290 x 2796 — same shape, very different sharpness. A screen size calculator tells you how big the glass is in inches; a ratio calculator tells you what shape it is. They answer different questions.

You do not need software to reduce a resolution to a ratio, but the arithmetic is easy to round the wrong way, especially on an ultrawide panel whose label is not the true fraction. Three steps, done by hand:

1. Write the resolution as width over height — for a 3440 x 1440 monitor that is 3440 / 1440.
2. Find the greatest common divisor of the two numbers, the largest whole number that divides both evenly.
3. Divide both numbers by that divisor. What remains is the smallest whole-number ratio.

Worked examples

3440 x 1440: the greatest common divisor is 80, so 3440 / 80 = 43 and 1440 / 80 = 18, giving 43:18. Vendors call this '21:9' because 43 / 18 = 2.389 is close to 21 / 9 = 2.333 — but the real panel is 43:18, not 21:9. A second common ultrawide, 2560 x 1080, has a greatest common divisor of 40, so 2560 / 40 = 64 and 1080 / 40 = 27, giving 64:27 (64 / 27 = 2.370). Both monitors are sold under the same '21:9' banner while their panels are two different fractions. Use the screen ratio calculator above and it reports 43:18 or 64:27 directly, with the closest common ratio named alongside.

The phone examples reduce exactly: 1080 x 2340 divided by 120 is 9:19.5, and 1080 x 2400 divided by 120 is 9:20. The ultrawide rows do not — 3440 x 1440 reduces to 43:18, and the 5120 x 1440 super-ultrawide reduces to 32:9. That gap between the label and the maths is exactly what the misconceptions section below untangles.

The calculator needs the resolution, not the diagonal. If you only know the inches, find the resolution first using the method for your system:

Windows

Open Settings, choose System, then Display. The active monitor shows its resolution under 'Display resolution'. Alternatively, right-click the desktop and open Display settings.

macOS

Click the Apple menu, choose About This Mac, then Displays. The resolution is listed there; in newer macOS it also appears under System Settings, Displays.

Any browser

Open the developer tools (F12), and in the console type window.screen.width + 'x' + window.screen.height to read the screen's pixel resolution directly.

Screen size is a diagonal measurement in inches and has nothing to do with the ratio. A 24-inch and a 32-inch monitor can be the same 16:9 shape; the size only changes how large each pixel is. So 'what ratio is my 27-inch monitor' cannot be answered from the inch number alone — you need the resolution, which is why the find-your-resolution steps below come first.

Once you know the ratio, the dedicated calculators work the shape out in detail with resolution tables and worked examples. The links below cover the ratios most screens actually use.

• 16:9 calculator
• 21:9 calculator
• 16:10 calculator
• Aspect ratio converter
• Image aspect ratio checker
• Embeddable calculator

The aspect ratio calculator names the shape a size already is, and the common ratios table lists every ratio on one page.

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