Image Aspect
Ratio Calculator

What Is an Aspect Ratio?

The aspect ratio of an image is the relationship between its width and its height. It is written as two numbers separated by a colon, such as 16:9 or 4:3. A ratio of 16:9 means that for every 16 units of width the picture has 9 units of height. The ratio does not tell you how many pixels the image has. A tiny 160 x 90 picture and a huge 3840 x 2160 picture are both 16:9, because they have exactly the same shape.

Knowing the aspect ratio matters whenever an image has to fit a frame: a website banner, a video player, a phone screen, a print or a social media post. If the shape of your picture does not match the shape of the space, the platform will crop it, stretch it or add empty bars. An image aspect ratio calculator helps you avoid all three problems.

How to Calculate the Aspect Ratio of an Image

To find the aspect ratio, divide the width and the height by their greatest common divisor. For example, take an image that is 1920 x 1080 pixels. The greatest common divisor of 1920 and 1080 is 120. Dividing both numbers by 120 gives 16 and 9, so the aspect ratio is 16:9. The decimal form of the same ratio is simply width divided by height, which is 1.778 in this case.

Doing this by hand is slow when the numbers are awkward, such as 2736 x 1824. This calculator does the work instantly, shows the simplified ratio, the decimal value, the orientation and the megapixels, and even suggests the closest common ratio when the exact ratio is unusual.

How to Use This Image Aspect Ratio Calculator

1. Find the aspect ratio of an image

Open the Find aspect ratio tab and type the width and height in pixels. You can also press Use the size of my image and pick a file from your device. The tool reads only the pixel size, and the file stays on your device. The result appears at once, together with a small preview box that shows the shape of the image.

2. Resize an image and keep the same ratio

Open the Resize with the same ratio tab and enter the original width and height. Then type a new width and the calculator fills in the matching height, or type a new height and it fills in the width. This is the quickest way to find a size that will not stretch or squash your picture.

3. Try a common ratio

Select one of the ratio buttons, such as 16:9, 4:3, 1:1 or 9:16, to see what height matches your width for that shape. This is helpful when you plan a design for a specific screen or platform before you start working.

Common Aspect Ratios and Where They Are Used

How to Resize an Image Without Stretching It

Stretching happens when you change the width and the height by different amounts. To avoid it, keep the ratio fixed. The formula is simple: new height equals new width multiplied by the original height and divided by the original width. If your picture is 4000 x 3000 and you want it 1200 pixels wide, the new height is 1200 × 3000 ÷ 4000, which is 900 pixels. The calculator applies this formula as you type.

Always resize from a large original down to a smaller size. Making a small picture bigger forces software to invent pixels, and the result looks soft. If you need to shrink the file as well as the dimensions, use our Compress Image to Exact KB tool afterwards.

Aspect Ratio vs Resolution

Resolution is the number of pixels in the image, for example 1920 x 1080. Aspect ratio is only the shape. Two images can have the same resolution and a different shape, such as 1200 x 800 and 960 x 1000 pixels, which both hold about one megapixel. They can also have the same shape and very different resolutions. When a design brief asks for a ratio, you need the shape. When it asks for a size, you need the pixels. For print work you also need the density, which you can check with our Image DPI Calculator.

What to Do When Your Image Does Not Match the Ratio

Sometimes your photo has one shape and the place you want to use it has another. You have three choices. You can crop the picture so it fills the new shape, which removes some of the edges. You can fit the whole picture inside the new shape and fill the empty space with a background colour or blur. Or you can stretch the picture, which is almost never a good idea because faces and logos become distorted. Cropping and padding both keep the proportions natural.

For social media sizes, our Social Media Image Resizer offers ready presets for Facebook, Instagram, YouTube, TikTok, X, LinkedIn and Pinterest and lets you choose between cropping and padding.

Aspect Ratio Tips for Websites, Video and Print

• Websites: Set the width and height attributes, or the CSS aspect-ratio property, so the page does not jump while images load. This improves layout stability.
• Video: 16:9 is the standard for landscape video and 9:16 for vertical video. Uploading the wrong shape adds black bars.
• Print: Photo paper sizes have their own ratios. A 4 x 6 inch print is 3:2, an 8 x 10 inch print is 5:4. Crop your photo to the paper ratio before ordering.
• Thumbnails: Design for the safe centre of the picture, because platforms often crop the edges on small previews.

Free, Private and Instant

This image aspect ratio calculator is free to use, needs no sign-up and works on phones, tablets and computers. All calculations happen inside your browser, so your pictures are never sent to a server. Bookmark the page and use it whenever you need to check a ratio or work out the right size for a new design.