Aspect Ratio Calculator

Solve for the missing width or height at a fixed ratio, or paste a list of sizes and read back what ratio each one already is.

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What this tool does

Aspect Ratio Calculator works in two directions, and which one you get depends on whether the input box holds a size. Leave it empty and the fields on the right solve a proportion: choose a ratio, say whether you know the width or the height, type that number, and the other side comes back. Put a size in the box and the tool switches to identification — every line that is not blank and does not start with # or // is read as a size, and the ratio settings are ignored for that run.

Solving gives you more than the one number. The result states the ratio as a decimal, the opposite side to two decimal places, the same figure rounded to whole pixels, and the total pixel count in millions. Two decimals is the ceiling, so a height of 768.375 is printed as 768.38 and a print-sized total lands on 0 MP; where the rounding matters the whole-pixel line says so, as with 1366 at 16:9, rather than quietly presenting itself as exact. Underneath sits a table of common sizes at your chosen ratio, stepped by width from 320 to 7680 for landscape and square ratios, or by height from 480 to 3840 for portrait ones.

Identification is the half people reach for when auditing a folder of screenshots or exports. Write one size per line as 1920x1080, 1366 × 768 or 24 x 36, optionally prefixed with a label as in Poster: 24 x 36, and each row comes back with the ratio reduced by greatest common divisor, the decimal to four places, the orientation and the pixel count. A Closest common column matches the decimal against sixteen familiar ratios within a two per cent tolerance, marking an inexact match with ≈ — which is why 1366 × 768 reports as 683:384 and ≈ 16:9 at the same time, both of which are true.

The arithmetic assumes square pixels, and that is the assumption to check before trusting an answer about video. A 720 × 576 frame is reported as 5:4 because that is its storage ratio; anamorphic material carries a pixel aspect ratio flag that makes the same frame display as 4:3 or 16:9, and nothing here reads that flag. The tool also stops at the number. It will not fit one ratio inside another, so it cannot tell you how deep the letterbox bars are when 2.39:1 footage sits in a 16:9 frame, and it alters no files at all. Everything happens in this browser tab, and no image or video is uploaded, because none is involved.

How to use it

  1. Choose the ratio. The menu offers 16:9, 4:3, 3:2, 1:1, 16:10, 21:9, 9:16, 4:5 and 2:3. Custom reveals a field that accepts 5:4, 2.39:1, or a bare decimal such as 1.85.
  2. Say which side you already know. Pick Width or Height and the matching number field appears. The value has to be greater than zero; a blank or a zero is refused rather than treated as one.
  3. Read the missing side. You get the figure to two decimals, the whole-pixel equivalent, the total in megapixels, and a table of standard sizes at the same ratio to pick a sensible export from.
  4. Or paste sizes to identify them instead. One per line, separated by x, ×, * or a plain space. Lines beginning with # or // are skipped, so a list can carry notes, and a line the parser cannot read stops the run and names its number.

Processing & privacy

Runs on your device. Your file is processed directly in this browser.

Common use cases

Sizing artwork for a slide or a video frame

You know the 1920 px width the deck uses and need the height that keeps 16:9 without the renderer padding or squashing your image.

Cutting a vertical version of a horizontal edit

Switch the ratio to 9:16, enter the height you are exporting at, and take the width before you set up the crop in an editor.

Auditing a folder of exports

Paste every size you have as a batch and read one table back. A file that comes out 683:384 rather than 16:9 is the one that was resized by hand.

Ordering a print at a fixed proportion

The fields are labelled px but the maths is unitless, so 24 in one side at 2:3 gives 36 in the other just as readily as pixels.

Questions

Do the numbers I type leave this tab?
No. Aspect Ratio Calculator is arithmetic on numbers you type, done in this browser tab. Nothing you type is transmitted or saved anywhere, and the page keeps working with the network disconnected.
Why is 1366 × 768 shown as 683:384 rather than 16:9?
Because 683:384 is the exact reduction — 1366 divided by 768 is 1.7786, and 16:9 is 1.7778. The two are close enough for the Closest common column to report ≈ 16:9, but they are not the same ratio, which is why a 1366 × 768 panel is a hair wider than true 16:9 instead of matching it.
Why don't the whole pixels divide evenly?
Most ratios cannot be hit exactly at an arbitrary size. The two-decimal value is shown on the line above the whole-pixel one, and the whole-pixel line is labelled as rounded whenever the two differ, so you can decide whether to nudge the known side to a figure that divides cleanly.
What does the Closest common column mean when it shows a dash?
That the decimal is more than two per cent away from all sixteen ratios in the reference list, which runs from 1:1 through 3:2, 16:10, 1.85:1 and 2.39:1 to 32:9 and 9:16. A dash means the size is unusual, not that it is wrong.
Does this resize my image?
No, it returns numbers only. Take the width and height it gives you to Resize Image to change an image's pixel dimensions, Crop Image to cut a frame to a preset proportion, or Crop Video for a moving one.
Why is "1920 by 1080" rejected?
The size parser takes a single separator character, so the word by is not one it accepts. Write the two numbers apart with x, ×, * or a space — 1920x1080, 1920 × 1080 or 1920 1080 all parse — and note that negative numbers and sizes with units attached, such as 1920px x 1080px, are refused as well. The Custom ratio field is looser and does read 16 by 9, which is an inconsistency between the two parsers rather than a rule worth relying on.

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