Aspect Ratio Calculator

Work out an aspect ratio and resize without stretching

Aspect Ratio Calculator does two jobs. Find the ratio reduces any width and height to their simplest whole-number ratio — 1920 × 1080 becomes 16:9 — and tells you which common ratio it matches or comes close to. Resize keeps a ratio fixed while you change one side, so you get the other side without distorting the picture.

Results update as you type, and a small rectangle shows the shape of each ratio. The calculations happen in your browser and nothing is uploaded.

How to find and use an aspect ratio

1. Under Find the ratio, enter the width and height — pixels, centimetres or any unit, as long as both are the same.
2. Read the simplified ratio, its decimal form and the note on the nearest common ratio. Use the copy buttons to copy either form.
3. Under Resize, pick a ratio from the list or choose Custom and enter your own, or press Use this ratio to resize to bring across the one you just found.
4. Type a new width to get the height, or a new height to get the width. The box you didn’t type in fills in automatically.
5. Tick Round to even numbers if the size is for video, then press Copy size to copy it as width x height.

Understanding the ratio and the resized size

• Ratio: both sides divided by their greatest common divisor. The arithmetic uses whole numbers of any size, so large values are exact.
• Decimals: sizes such as 8.5 × 11 are scaled up to whole numbers first (85 × 110) and then simplified, giving 17:22. Up to six decimal places are used.
• Decimal form: width divided by height to two decimal places, written as 1.78:1. Portrait sizes give a number below 1.
• Common ratio note: says when the size is exactly a familiar ratio, or within 3% of one — 1366 × 768 simplifies to 683:384, which is shown as close to 16:9.
• Resized size: the calculated side is rounded to whole pixels, or to the nearest even number when that option is on. The note underneath gives the exact value before rounding.

Typical aspect ratio jobs

• Video: pick an export size that keeps 16:9, or 9:16 for vertical video, with even dimensions for the encoder.
• Social media images: size a picture for a 1:1 or 4:5 post before you crop it with the Image Cropper.
• Web layouts: find the ratio of an image or embed so you can reserve its space with the CSS aspect-ratio property.
• Scaling images: work out the height for a new width, then resize the file with the Image Resizer.
• Screens and prints: see whether a monitor resolution or a paper size matches a common ratio.

Getting clean numbers

• If the simplified ratio has large numbers, like 683:384, the size isn’t an exact common ratio. The note shows which one it is close to.
• When resizing, choose a width that divides evenly by the ratio’s first number (for 16:9, a multiple of 16) and the height comes out whole with no rounding.
• Rounding to whole pixels changes the ratio very slightly. For most images this is invisible, but the exact value in the note tells you how far off it is.

Aspect ratios explained

What an aspect ratio describes

An aspect ratio is the relationship between width and height, not the size itself. A 1280 × 720 video and a 3840 × 2160 one are both 16:9: one is just a larger copy of the other. Keeping the ratio when resizing is what stops faces and circles looking stretched or squashed.

Why 21:9 screens are not exactly 21:9

“21:9” is a marketing name for ultrawide screens. Their real resolutions, such as 2560 × 1080 (64:27) and 3440 × 1440 (43:18), are close to 21:9 but not equal to it, which is why the calculator shows them with ≈.

Aspect Ratio Calculator: common questions