Free aspect ratio calculator — get the exact ratio of any width and height, resize without stretching, and turn a screen diagonal into real width and height.
aspect-ratio: 16 / 9;
padding-bottom: 56.25%;
| Resolution | Known as | Pixels |
|---|
The exact ratio comes first — anything rounded is labelled as rounded, with the difference shown.
The page has three tabs because “aspect ratio” is asked in three different shapes. Each one is independent, so switching tabs never disturbs what you left in another.
An aspect ratio is the relationship between width and height, written as two numbers with a colon between them. It describes shape and nothing else. 1280×720, 1920×1080 and 3840×2160 are all 16:9, so all three are the same shape and differ only in how many pixels fill it.
Getting the ratio is one division. Find the largest number that divides into both the width and the height — the greatest common divisor — and divide both by it. For 1920 and 1080 that number is 120: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, giving 16:9. This calculator does exactly that on whole numbers, so what you get back is the true ratio in its lowest terms — the same thing as simplifying a fraction — and not a decimal dressed up to look like one.
That distinction matters more often than you would think. A 1366×768 laptop panel is sold as 16:9, but its exact ratio is 683:384 — about 0.05% away from 16:9, which is invisible, but not the same number. Where the two differ, this page shows the exact ratio first and then names the standard one it is close to, along with how far apart they are, rather than quietly rounding on your behalf.
| Ratio | Decimal | Where you meet it |
|---|---|---|
| 1:1 | 1.0000 | Square social posts, avatars, album covers |
| 4:5 | 0.8000 | The tallest portrait post the Instagram feed allows |
| 5:4 | 1.2500 | Older 1280×1024 office monitors |
| 4:3 | 1.3333 | Pre-widescreen televisions, iPads, many compact cameras |
| 3:2 | 1.5000 | 35mm film, most mirrorless and DSLR sensors, Surface laptops |
| 16:10 | 1.6000 | Many premium laptop and monitor panels, and MacBooks before the notch |
| 16:9 | 1.7778 | HD and 4K video, TVs, most monitors and displays, YouTube |
| 1.85:1 | 1.8500 | Cinema “flat” projection |
| 21:9 / 43:18 | 2.3333 / 2.3889 | Ultrawide monitors — 3440×1440 is really 43:18 |
| 2.39:1 | 2.3900 | Cinema “scope”, the widest common film shape |
| 32:9 | 3.5556 | Super-ultrawide monitors such as 5120×1440 |
| 9:16 | 0.5625 | Stories, Reels, TikTok, Shorts — 16:9 stood upright |
To resize a photo, an image or a video and keep it looking right, both dimensions have to change by the same factor. Halve the width and you must halve the height. Change only one and the picture is squashed or stretched, which is obvious on faces and on circles long before it is obvious anywhere else.
The arithmetic is a single cross-multiplication. New height = new width × old height ÷ old width. Going from 1920×1080 to 1280 wide gives 1280 × 1080 ÷ 1920 = 720. The Resize tab runs it in both directions, so you can drive it from whichever side you actually have a constraint on.
Most ratios do not divide evenly into most widths. 1920×1080 scaled to 1000 pixels wide wants a height of 562.5, and image files have no half pixels. The tool rounds to 563, tells you it rounded, states the ratio 1000×563 really has, and offers the nearest sizes that are exact multiples of 16:9 — useful when a video encoder or a print job insists on clean numbers.
A TV, monitor or any other display is sold by its diagonal, which tells you almost nothing on its own about how much wall or desk they need. The diagonal, the width and the height form a right-angled triangle, so scale the ratio until its own diagonal matches the quoted figure and the real sides fall out.
A 55″ 16:9 television is about 47.94″ wide and 26.96″ tall — about 121.8 × 68.5 cm of panel, before the bezel and the stand. A 27″ 16:9 monitor is about 23.53″ by 13.24″.
The catch worth knowing is that the same diagonal does not mean the same area. The further a rectangle is from square, the less area a given diagonal encloses. A 49″ 32:9 super-ultrawide has substantially less screen than a 49″ 16:9 television, because it is far shorter for the same corner-to-corner measurement. The Screen Size tab prints that comparison next to whatever ratio you enter, so the difference is a number and not a surprise after delivery.
On the web, aspect-ratio: 16 / 9; tells the browser to hold a box in that shape
however wide it ends up, which is what keeps embedded video and image placeholders from
jumping about as a page loads. Every current browser supports it.
The older method is a percentage of padding-bottom on an empty box, because
vertical padding percentages are measured against the element’s width. For
16:9 that percentage is 9 ÷ 16 = 56.25%. The Find the Ratio tab
prints both lines for whatever shape you have entered, ready to copy.
| Where | Ratio | Usual pixel size |
|---|---|---|
| YouTube video | 16:9 | 1920×1080 or 3840×2160 |
| YouTube thumbnail | 16:9 | 1280×720 |
| Instagram feed, square | 1:1 | 1080×1080 |
| Instagram feed, portrait | 4:5 | 1080×1350 |
| Stories, Reels, TikTok, Shorts | 9:16 | 1080×1920 |
| Presentation slide | 16:9 | 1920×1080 |
| Desktop wallpaper | 16:9 | 1920×1080 or 3840×2160 |
| Ultrawide wallpaper | 43:18 | 3440×1440 |
Upload something in the wrong shape and the platform will either add bars around it or crop it, and neither choice is yours. Getting the ratio right first is cheaper than arguing with an automatic crop afterwards.
Every calculation on this page happens in your browser. When you use Choose an image, the browser reads that file’s width and height on your own device and hands back two numbers — the picture itself is never sent anywhere, never stored, and never seen by us. Once the page has loaded it works with no connection at all.