design tool

Aspect ratio calculator

Type a width and a height and the shape is drawn, not just described. Pick something to compare it against and the same picture shows both answers at once: the bars you get if you fit the design whole, and the part that is cut away if you fill the frame instead.

Runs on your device. Nothing is uploaded.

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How to use it

  1. 1

    Type the size you have

    Width and height, in pixels, millimetres or anything else. The ratio, the decimal and the named shape update as you type.

  2. 2

    Choose what to compare it against

    Common ratios, ISO and US paper, screen and video sizes, and the ten canvases the flyer builder actually offers. Custom is at the bottom of the list.

  3. 3

    Read the drawing

    The outlined frame is the target. The tinted block is your design fitted whole inside it. The dashed outline is the same design enlarged to fill the frame, so anything outside the frame is what gets cropped.

  4. 4

    Apply the matching size

    One button offers the size that would make your shape match the target, keeping whichever dimension you typed last. Tapping it fills the boxes in.

Two rectangles beat four numbers

Most ratio calculators hand back a number and leave you to imagine what it means. A shape is easier to judge by looking at it. Drawing your rectangle inside the target rectangle answers the two questions people actually have, which are how much empty band appears if the whole design has to fit, and how much of the picture disappears if it has to reach the edges. Both are in the same picture, so there is nothing to switch between.

Messy sizes get a straight answer

A frame exported two pixels short is a common accident. Reducing 1918 by 1080 to lowest terms gives 959:540, which is arithmetically correct and completely useless. It is 0.1 per cent away from 16:9, so that is what the tool says, with the raw reduction shown underneath for anyone who wants it. The same rule catches sizes that are close to 4:3, 3:2 and the ISO paper ratio of one to the square root of two.

Where the presets come from

The ISO A series runs from A0 at 841 by 1189 millimetres down to A6, every sheet sharing the same one to 1.414 shape, which is why halving one gives the next. US Letter, Legal and Tabloid follow the ANSI series. The screen sizes are the standard broadcast and display resolutions. The last group is the ten canvases this product's flyer builder offers, at the exact pixel sizes it uses, so a size named here is the size that comes out.

Scaling is not converting

Two shapes that differ cannot be scaled into each other. Something has to give, and it is either an empty band or a piece of the design. The percentages in the readout tell you which trade you are making and how expensive it is. When the loss is large, the honest answer is to lay the content out again at the new shape rather than crop, and the numbers here are what you need to start that.

Limits

  • Sizes are rounded to whole numbers, which only matters at very small dimensions.
  • A ratio has no units, so comparing 1920 pixels against 210 millimetres is a comparison of shape only.
  • The nearest named shape is reported when the exact fraction is within about one and a half per cent.

What it does not do

  • It does not resize, crop or export an image.
  • It does not relay out a design for a new shape, which is design work rather than arithmetic.
  • It does not know what a platform will do to a file after you upload it.

Questions people ask

What ratio is a widescreen video?

Sixteen to nine, which is 1.778 as a decimal. At 1080p that is 1920 by 1080 pixels and at 4K it is 3840 by 2160. Vertical video is the same shape turned around, nine to sixteen, most commonly 1080 by 1920. All three are in the compare list, along with the cinema ratios.

My image is 1918 by 1080. Why does it say 16:9?

Because it is, to within a tenth of a per cent. Reduced properly it is 959 to 540, a fraction nobody recognises, produced by a crop that lost two pixels somewhere. The tool reports the named shape when the difference is under about one and a half per cent, and prints the exact reduction underneath so you can see what happened.

Can I compare pixels against millimetres?

Yes, because a ratio has no units. A 1920 by 1080 frame and an A4 sheet are different shapes regardless of what you measure them in, and the drawing shows exactly how different. The bar and crop figures come out as percentages for that reason, since a percentage of the target frame means the same thing in either unit.

What is the aspect ratio of A4 paper?

One to the square root of two, about 1 to 1.414, which every sheet in the ISO A series shares. That is the point of the series: halving a sheet along its long side gives the next size down at the same shape. A4 is 210 by 297 millimetres and A0 is 841 by 1189.

Which social post shape should I use?

A taller post takes up more of a phone screen while somebody scrolls, which is the mechanical reason four to five tends to hold attention longer than a square. It is a tendency rather than a rule, and it will not rescue a weak first frame. Both shapes are in the compare list, along with the story and cover sizes.

Does the calculator send my numbers anywhere?

No. The arithmetic and the drawing both happen in this page, and no network request is made after it loads. There is nothing to store, nothing to upload and no account. That is true of every tool here, and it is why an unpublished campaign is safe to work out sizes for.

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Related tools

Background reading: the question page on this.

Sources

Written and checked by the OneCraft team. Last checked .