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Aspect Ratio Calculator

Calculators · Added

Three related questions with one piece of arithmetic behind them: what ratio is this size, what is the other dimension if I set this one, and what happens when a picture of one shape meets a box of another. The ratio is reduced by its greatest common divisor, so 1920 × 1080 comes back as 16:9 rather than as itself.

What do you need
px
px
px

Leave empty to solve for it.

px

Fill in one of the two, not both.

Standard aspect ratios

RatioAs a numberWhere you meet it
1:11.000Square — profile photos, Instagram posts
5:41.2508×10 print
4:31.333Compact cameras, older monitors, iPad
3:21.50035 mm film and most DSLR sensors
16:101.600Many laptop displays
16:91.778HD and 4K video, most monitors and TVs
2:12.000Univisium, some social banners
21:92.333Ultrawide monitors (2.33:1)
2.39:12.390Anamorphic cinema scope
9:160.563Phone screens, Reels, Shorts, Stories
4:50.800Instagram portrait
2:30.667Portrait 35 mm, 4×6 print
3:40.750Portrait 4:3

How to use the aspect ratio calculator

  1. 1Enter the original width and height in pixels — or any consistent unit, since a ratio has none.
  2. 2For a resize, fill in either the new width or the new height and leave the other empty.
  3. 3For the ratio alone, switch to Find the ratio: you get the simplified form, the decimal and the nearest standard.
  4. 4For Fit in a box, add the box dimensions to see both the fitted and the filled result.
  5. 5Read the note under the answer — it says whether the rounded pixel size is exactly on the ratio.

Examples

Scaling a video frame

Input
1920 × 1080, new width 1280
Result
1280 × 720 — 66.67% scale, still 16:9

Both are exactly 16:9, which is why the height lands on a whole number. Not every target width does.

Identifying an odd size

Input
1366 × 768
Result
683:384 — nearest standard 16:9, off by 0.05%

The reduced ratio looks nothing like 16:9, but numerically it is within a twentieth of a per cent. This is the classic laptop panel size.

A landscape photo in a social banner

Input
4000 × 3000 into 1200 × 628
Result
Fit: 837 × 628 · Fill: 1200 × 900, cropping 272 px of height

A 4:3 photo in a roughly 1.91:1 box: either bars down the sides or a crop off the top and bottom. There is no third option.

About the aspect ratio calculator

Why ratios are written the way they are

An aspect ratio is width compared to height, reduced to the smallest whole numbers that express it. 1920 × 1080 divides by 120 to give 16:9. The reduction matters because it makes different sizes with the same shape obviously comparable — 1280 × 720, 2560 × 1440 and 3840 × 2160 all reduce to the same pair, which is exactly the fact you want when checking that a set of assets match.

Cinema uses a different convention and writes a single number against one: 2.39:1 rather than 239:100. It reads better for the very wide formats and it hides the arithmetic, which is why the decimal form appears alongside the reduced form here. Both are shown because both turn up, and converting between them by hand is the sort of small friction that produces mistakes.

Some real sizes reduce to nothing useful. 1366 × 768 comes out as 683:384, because 683 is prime. The size exists for manufacturing reasons rather than mathematical ones, and treating it as 16:9 — which it is to within 0.05% — is what everyone does in practice. That is why the nearest standard ratio is reported with the error beside it rather than silently rounded to the friendly answer.

Where getting this wrong shows

The most visible failure is stretching: setting both a width and a height that do not match the original shape, so faces come out wide or narrow. It is instantly recognisable and completely avoidable — set one dimension, let the other follow. This tool refuses to accept both for exactly that reason, and points at the fit mode instead when a box is genuinely fixed.

The second is the silent crop. Upload a tall portrait photograph as a wide banner and the platform will centre and cover it, cutting the top and bottom, which is where heads and captions usually are. Knowing before you upload how much will be removed — the figure this tool gives in fill mode — turns that from a surprise into a decision about where to place the subject.

The third is mismatched assets in a set. Thumbnails generated at slightly different ratios sit in a grid with uneven gaps, and the cause is almost always one image rounded a fraction differently from the rest. Working out the target size once, checking it reduces to the ratio you meant, and applying it to everything is the fix.

Frequently asked questions

Why does the new height come out with a decimal?
Because not every width sits exactly on the ratio. A 16:9 shape needs the width to be a multiple of 16 for the height to land on a whole number, so scaling to 1000 px wide gives 562.5 px tall. Pixels do not come in halves, so something has to round, and the rounding moves the true ratio by a few hundredths of a per cent. That is invisible on screen and worth knowing when two images have to line up edge to edge.
What is the difference between fitting and filling?
Fitting scales the picture until it is entirely inside the box, so nothing is lost and empty space is left along one pair of edges — letterboxing. Filling scales until the box is entirely covered, so no space is left and whatever overflows the edges is cut off. In CSS these are the contain and cover values of object-fit and background-size. Which is right depends on whether the edges of the image carry anything you cannot lose.
Why are 16:9 and 16:10 so close and yet not interchangeable?
As decimals they are 1.778 and 1.600, which is a difference of about eleven per cent in height — small enough to look similar in a specification and large enough to be obvious on screen. A 16:9 video played full-screen on a 16:10 display leaves visible bars top and bottom. The reason both exist is that 16:10 was favoured for desktop work, where vertical space is useful, while 16:9 followed broadcast video and eventually won on price.
Does this change my image file?
No. This is arithmetic on the numbers you type, and it produces the dimensions to use — nothing is opened, written or uploaded. To actually resize a file, use the image resizer, which does the work on a canvas inside your browser, or the cropper if the shape needs to change rather than the size. This tool is the step before either of those, for working out what the target numbers should be.

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