A screen's advertised size is only the diagonal, which tells you surprisingly little about how big it actually is on your desk. The width, height, and surface area are what decide whether a monitor fits your space and how large the picture feels. Use the calculator below to turn any diagonal and aspect ratio into exact dimensions, then read on to understand what the numbers mean.
≈ 59.7 × 33.6 cm
Monitors and TVs are sold by their diagonal, the distance from one corner to the opposite corner. That single number hides the dimensions you actually care about: how wide the screen is, how tall it is, and how much surface area it covers. Two screens with the same diagonal can have very different widths if their aspect ratios differ.
On a standard 16:9 screen, the width is only about 87% of the diagonal and the height about 49%. So a 27-inch monitor isn't 27 inches wide, it's about 23.5 inches wide and 13.2 inches tall. The calculator above does this conversion instantly, but the takeaway is simple: never assume the diagonal is the width.
The tool needs just two inputs, and a third optional one for sharpness:
From those, it calculates the exact width, height, and area in both inches and centimeters, plus the PPI if you supply a resolution. It's the fastest way to check whether a monitor will physically fit a desk, a shelf, or a dual-monitor setup before you buy.
The calculator uses the aspect ratio and the Pythagorean theorem to split the diagonal into width and height. For any aspect ratio written as w:h, the width equals the diagonal times w divided by the square root of (w squared plus h squared). The height swaps in h on top.
For a 16:9 screen, that square root is about 18.358. So the width is the diagonal times 16 divided by 18.358 (roughly 0.8716 of the diagonal), and the height is the diagonal times 9 divided by 18.358 (roughly 0.4903). Multiply width by height and you get the area. The tool runs all of this so you never touch the formula.
Here are the actual width and height for the most common 16:9 monitor sizes, the ones you'll see most often when shopping. Notice how the width grows more slowly than you might expect as the diagonal climbs.
| Diagonal | Width | Height | Area |
|---|---|---|---|
| 24 inch | 20.9 in | 11.8 in | 246 in² |
| 27 inch | 23.5 in | 13.2 in | 311 in² |
| 32 inch | 27.9 in | 15.7 in | 438 in² |
| 34 inch (21:9) | 31.4 in | 13.1 in | 411 in² |
The 34-inch ultrawide is the interesting row. Its diagonal is larger than the 32-inch 16:9, yet it's actually shorter in height, because the 21:9 shape trades vertical space for width. That's exactly the kind of surprise the calculator helps you avoid.
When you compare screen sizes, the diagonal undersells the real difference, because area grows with the square of the size. A 32-inch monitor sounds only a little bigger than a 27-inch, but it actually has about 40% more surface area, a much larger jump than the 19% bigger diagonal suggests.
| Step up | Diagonal increase | Area increase |
|---|---|---|
| 24 to 27 inch | +12.5% | +26% |
| 27 to 32 inch | +18.5% | +41% |
| 24 to 32 inch | +33% | +78% |
This is why jumping two sizes feels dramatic. Going from a 24-inch to a 32-inch nearly doubles the glass in front of you. Keep this in mind when budgeting desk space: a screen that's "just a few inches bigger" can dominate a small desk.
Aspect ratio reshapes a screen even when the diagonal stays the same. A 21:9 ultrawide and a 16:9 standard monitor at the same diagonal cover similar area but distribute it very differently, one favoring width, the other height.
| 34-inch screen | Width | Height |
|---|---|---|
| 21:9 ultrawide | 31.4 in | 13.1 in |
| 16:9 standard | 29.6 in | 16.7 in |
So an ultrawide buys you about 2 extra inches of width but gives up about 3.6 inches of height. If your work is spreadsheets and timelines, the width wins. If it's reading and coding, the extra height of 16:9 can matter more. Our ultrawide resolution guide covers which resolutions suit each shape, and the aspect ratio guide explains the shapes themselves.
Physical size is only half the story. The same resolution looks sharper on a smaller screen and softer on a bigger one, because the pixels spread out. That's why the calculator also reports pixel density (PPI) when you enter a resolution alongside the size.
For example, 1440p looks crisp at 109 PPI on a 27-inch screen but drops to a softer 92 PPI when stretched to 32 inches. If you're sizing up a monitor, check both the physical dimensions here and the density, so you don't end up with a big screen that looks fuzzy. Our PPI calculator focuses purely on that sharpness side, and the pixel density guide explains the thresholds.
A common use is checking whether a monitor physically fits before buying. Here's the quick workflow:
For a dual-monitor setup, double the width and add a small gap. Two 27-inch 16:9 monitors side by side need about 47 inches plus stands, which surprises a lot of people with smaller desks. The calculator catches that before the boxes arrive.
If you shop or measure in metric, the calculator shows every dimension in centimeters too. The conversion is simply inches times 2.54, but having it done for you saves errors. A 27-inch diagonal is about 68.6 cm, with a width near 59.7 cm and a height near 33.6 cm.
This matters most for fitting a screen into furniture measured in centimeters, like a TV cabinet or a shelf. Reading both units side by side means you never mix up a measurement when you're standing in a store or comparing listings from different regions.
Once you know a screen's real dimensions, the natural next question is which resolution suits it. As a rough guide: 1080p suits up to about 24 inches, 1440p shines around 27 inches, and 4K earns its keep from 27 inches and up. Those pairings keep pixel density in the comfortable 90-to-140 PPI band.
Go too big for the resolution and the image softens; go too small and you're paying for pixels you can't see. The calculator's optional PPI readout lets you test any pairing instantly. For the full standards behind each resolution, see our screen resolution guide and the sortable resolution chart.
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