Aspect Ratio Calculator

What this tool does

Enter a width and height to get the simplified aspect ratio and decimal ratio, or lock a ratio and type one new dimension to find the other. Useful for resizing images, photos, and print layouts without distortion.

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Find and keep any aspect ratio

The aspect ratio of an image or page is the relationship between its width and its height, written as two numbers such as 16:9 or 4:3. This calculator does two jobs: it reduces any width and height to their simplest ratio, and it scales one side to match a ratio so the other side follows automatically. That means you can resize a photo, a video frame, or a print layout without squashing or stretching it.

Type a width and a height to see the simplified ratio (for example 1920 x 1080 becomes 16:9) along with the exact decimal value. Switch to resize mode, lock the ratio, change the width, and the matching height appears instantly.

Why aspect ratio matters for printing

Standard photo and paper sizes each have a fixed ratio. A 4x6 print is 3:2, a 5x7 is 7:5, and A-series paper is 1:1.414. If your image ratio does not match the paper, part of the picture is cropped or you get white borders. Checking the ratio before you print saves wasted ink and paper.

3:2 — 35mm photos, 4x6 and 6x9 prints.
4:3 — older cameras, tablets, many projectors.
16:9 — widescreen video and monitors.
1:1 — square social posts and instant photos.
1:1.414 — A4, A3 and the whole A-series.

How to use the calculator

In ratio mode, enter the current width and height. The simplified ratio and decimal appear automatically.
In resize mode, set the ratio you want to keep (or carry over the one just calculated).
Type a new width to get the matching height, or a new height to get the matching width.
Use the values to resize in your editor or to pick the closest standard print size.

Worked example

You have a 4000 x 3000 pixel photo and want to print it without cropping. The calculator reduces 4000:3000 to 4:3. Looking at standard sizes, 4:3 is not a common print ratio, so you either crop slightly to 3:2 for a 6x4 print, or print at 4:3 with thin borders. Knowing the ratio first tells you exactly how much you would lose to a crop.

Notes and limitations

The simplified ratio uses the greatest common divisor, so 1920:1080 shows as 16:9 rather than 1920:1080.
Ratios are unitless — the same 16:9 works for pixels, millimetres, or inches.
This tool does not resize image files; it gives you the numbers to resize with in your own editor.

FAQs

Quick answers

What does an aspect ratio like 16:9 mean?

It means for every 16 units of width there are 9 units of height. The numbers describe the shape, not the size, so 16:9 is the same shape whether the image is 1600x900 or 1920x1080 pixels.

How do I resize an image without distortion?

Keep the aspect ratio fixed and change only one dimension; let the other follow. In resize mode, lock the ratio, type the new width, and use the height the calculator returns.

Which aspect ratio matches A4 paper?

The A-series uses a ratio of 1:1.414 (the square root of 2). That is why folding an A4 sheet in half gives two A5 sheets with the same proportions.

Why does my photo get cropped when I print it?

Because the photo's ratio does not match the print size. A 4:3 photo printed at 3:2 (6x4) must lose some height or width. Check the ratio first to see how much would be cropped.

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