Aspect Ratio Calculator

An aspect ratio is the shape of a picture or screen: how wide it is compared with how tall. This calculator works it out both ways. Type a width and height, such as 1920 × 1080, and it gives the simplest ratio (16:9), the same thing as a decimal, whether it is landscape or portrait, and the nearest well-known ratio when the numbers are not tidy. A 1366 × 768 laptop screen is really 683:384, which is about 16:9, and the page says exactly how close.

The second card keeps a ratio locked while you change the size. Type a new width and the height fills in, or type a height and the width follows. You can round to whole pixels, to even numbers for video, or to multiples of 8 or 16, which some encoders and design grids prefer, and the page tells you how far rounding moves you from the true shape. A live rectangle shows the shape, with a list of standard sizes at that ratio.

You can also open a photo or video to read its size. The file is read by your browser on your device and is never uploaded.

1. Type a width and height under “Find the ratio”, or tap “Read from a file” (or drop a file on the card) to fill them from a photo or video.
2. Read the simplest ratio, the decimal, and the closest common ratio. Tap “Copy ratio” to copy it.
3. Or tap a preset, such as “16:9”, “4:5 Instagram portrait” or “YouTube thumbnail”, to start from a standard size.
4. In “Resize, keeping the ratio”, type a new width or a new height. The other side fills in straight away.
5. Pick how to round under “Round to”, check the preview, then tap “Copy size” or a size under “Common sizes at this ratio”.

• Simplest whole-number ratio from any width and height, including decimals.
• Decimal ratio, orientation and megapixels.
• Nearest of 15 common ratios (from 1:1 to 32:9, plus A-paper) with the percentage difference and what it is used for.
• Locked-ratio resize from either side, with live results as you type.
• Rounding to whole pixels, even numbers, multiples of 8 or 16, or two decimals, with the error shown.
• 12 presets: 16:9, 9:16, 4:3, 1:1, 4:5, 3:2, 21:9, 16:10, 2.39:1, YouTube thumbnail, link preview and A4.
• Live rectangle preview and a clickable list of standard sizes for the current ratio.
• Reads the size of JPG, PNG, WebP, HEIC, TIFF, SVG and other images, plus MP4, MOV and WebM videos, on your device.

• Video files almost always need an even width and height. Choose “Even numbers (video)” before exporting so the encoder doesn’t add a black line or refuse the file.
• Phone photos are often stored sideways with a note saying which way is up. The size shown is the way the photo displays, which is what you want for posting.
• Instagram crops feed posts to between 1.91:1 and 4:5. A 4:5 portrait (1080 × 1350) takes up the most room in the feed.
• Changing the ratio of an image means cropping or adding bars; this tool only works out sizes. Use Crop Image or Resize Image to change the picture itself.