Aspect Ratio Calculator
Resolution to ratio, ratio back to pixels, and the pixel density of a screen.
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1920 × 1080 is exactly 16:9.
HD video and almost every television and monitor.
Resize keeping 16:9
height = 720 px
width = 1280 px
Both results are rounded to a whole pixel, because there is no such thing as a fraction of one. On a ratio that does not divide evenly that rounding can shift the true ratio by a hair — enough to leave a one-pixel bar if the result is being fitted into a fixed frame.
16:9 at common widths
| Width | Height |
|---|---|
| 640 px | 360 px |
| 1280 px | 720 px |
| 1920 px | 1080 px |
| 2560 px | 1440 px |
| 3840 px | 2160 px |
Pixel density
Screens are advertised by their diagonal, so the pixel diagonal has to be reconstructed before it can be divided by it.
Roughly 90–110 ppi is a conventional desktop monitor, 140+ is where individual pixels stop being visible at arm’s length, and phones run 400+ because they are held far closer. Print work is measured in DPI instead and is a different quantity — ink dots, not screen pixels.
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How it works
To find an aspect ratio, enter a width and height above — the resolution is reduced to its exact ratio by its greatest common divisor, shown against the nearest named ratio with the difference between them, and the panel underneath scales either dimension while keeping that ratio.
An aspect ratio is a fraction reduced to its lowest terms: divide the width and height by their greatest common divisor and you have it. 1920×1080 has a GCD of 120, giving 16:9. That much is arithmetic with no judgment in it.
The judgment is what to do with the resolutions that do not reduce neatly. 1366×768 — the most common laptop panel for a decade — reduces to 683:384, which is exact, correct, and useless to someone who wants to know whether their screen is 16:9. It is not quite: 683:384 is 1.7786 against 16:9’s 1.7778, a 0.05% difference, which is enough to leave a one-pixel bar when 16:9 content is displayed on it full-screen. So this calculator gives both — the exact reduction as the headline, the nearest named ratio beside it, and the error between them. Rounding silently to 16:9 hides a real difference; printing only 683:384 answers a question nobody asked.
The resize panel works the other way, holding the ratio and solving for the missing dimension. Results are rounded to a whole pixel because fractional pixels do not exist in a raster image, and on a ratio that does not divide evenly that rounding shifts the true ratio very slightly — which is worth knowing if the output is being fitted into a fixed frame.
Pixel density is a separate question that gets asked in the same breath. Screens are advertised by their diagonal, so the pixel diagonal has to be reconstructed with Pythagoras before dividing: a 27-inch 2560×1440 monitor is 108.8 ppi. Around 90–110 ppi is a conventional desktop display, 140 and up is where individual pixels stop being visible at arm’s length, and phones exceed 400 because they are held much closer.
Common resolutions and their ratios
Most video and display resolutions land on one of a handful of ratios. The ones that do not are usually older panel sizes that were approximating 16:9 within manufacturing constraints.
| Resolution | Aspect ratio |
|---|---|
| 1280 × 720 (720p) | 16:9 |
| 1920 × 1080 (1080p) | 16:9 |
| 2560 × 1440 (1440p) | 16:9 |
| 3840 × 2160 (4K UHD) | 16:9 |
| 4096 × 2160 (DCI 4K) | 256:135 (≈1.90:1) |
| 1366 × 768 | 683:384 (≈16:9) |
| 1920 × 1200 | 16:10 |
| 3440 × 1440 | 43:18 (≈21:9) |
| 1280 × 1024 | 5:4 |
| 1080 × 1920 (vertical video) | 9:16 |
16:9 dimensions at common widths
The heights that pair with a 16:9 width. Any width divisible by 16 gives a whole-pixel height, which is why standard resolutions cluster on those numbers.
| Width | Height at 16:9 |
|---|---|
| 640 px | 360 px |
| 1280 px | 720 px |
| 1600 px | 900 px |
| 1920 px | 1080 px |
| 2560 px | 1440 px |
| 3840 px | 2160 px |
| 7680 px | 4320 px |
Pixel density of common screens
Pixels per inch depends on resolution and physical size together, which is why a 4K 32-inch monitor is less sharp than a 4K 27-inch one despite having identical pixel counts.
| Screen | Pixel density |
|---|---|
| 24" 1920 × 1080 | 91.8 ppi |
| 27" 1920 × 1080 | 81.6 ppi |
| 27" 2560 × 1440 | 108.8 ppi |
| 32" 3840 × 2160 | 137.7 ppi |
| 27" 3840 × 2160 | 163.2 ppi |
| 13.3" 2560 × 1600 | 226.9 ppi |
FAQ
What is the aspect ratio of 1920 × 1080?
16:9 exactly. Both numbers divide by 120, giving 16 and 9 with nothing left over — which is why 1080p is the reference resolution for the ratio.
Is 1366 × 768 a 16:9 resolution?
Not exactly. It reduces to 683:384, which is 1.7786 against true 16:9’s 1.7778 — close enough to be marketed as 16:9, different enough to letterbox by a pixel when 16:9 content is shown full-screen.
How do I calculate an aspect ratio?
Divide the width and the height by their greatest common divisor. For 2560 × 1440 the GCD is 160, giving 16:9. The calculator above does this and also names the closest standard ratio when the reduction is not one.
What resolution is 21:9?
"21:9" is a marketing name; the actual ratio of a 3440 × 1440 ultrawide is 43:18, and of 2560 × 1080 it is 64:27. Neither is literally 21:9, which would be 7:3.
What is a good pixel density for a monitor?
Around 90–110 ppi is conventional and looks fine at normal desktop viewing distance. Above roughly 140 ppi individual pixels stop being distinguishable, which is what "retina-class" describes. Phones run 400+ because they are held far closer to the eye.
Is PPI the same as DPI?
Not quite. PPI counts pixels per inch on a screen; DPI counts ink dots per inch in print. The terms are used interchangeably in software, but a 300 DPI print target and a 300 PPI display are describing different physical things.