Aspect Ratio Calculator

What is aspect ratio?

An aspect ratio describes the shape of a rectangle by comparing its width to its height. It is written as two numbers separated by a colon, such as 16:9, 4:3, or 3:2. These numbers tell you how wide something is compared to how tall it is, but they do not specify an absolute size.

For example:

• 1920 × 1080 pixels and 3840 × 2160 pixels are both 16:9.
• 3000 × 2000 pixels and 600 × 400 pixels are both 3:2.
• 1080 × 1080 pixels, 2000 × 2000 pixels, and 5 × 5 inches are all 1:1.

If you change one side without adjusting the other side proportionally, the aspect ratio changes, and the content can look stretched or squashed. Keeping a consistent aspect ratio ensures that shapes and people look natural on different screens and print sizes.

How to calculate aspect ratio from width and height

The calculator does the math for you automatically, but the underlying steps are straightforward. Given a width w and a height h, you want to find the simplest whole-number ratio w_r : h_r that has the same proportion.

In mathematical terms, you divide both width and height by their greatest common divisor (GCD). This simplifies the pair to its smallest whole-number form while preserving the same relationship:

In plain language: divide both the width and the height by the same largest whole number that goes into both of them evenly.

Manual step-by-step method

1. Measure or look up the width and height. Use the same unit for both, such as pixels, millimeters, or inches.
2. Find a common divisor. Start with small numbers (2, 3, 4, 5, etc.) and see which one divides both width and height without leaving a remainder.
3. Divide both numbers by that divisor. If possible, repeat with larger divisors until you can no longer simplify.
4. Express the result as W:H. The simplified pair gives you the aspect ratio.

Worked example: 1920 × 1080

Suppose you have a video with a frame size of 1920 × 1080 pixels. To find its aspect ratio:

1. Start with the dimensions: 1920 (width) and 1080 (height).
2. Both numbers are divisible by 10, but you can simplify further. Compute the GCD, which in this case is 120.
3. Divide both by 120:
   1920 ÷ 120 = 16
   1080 ÷ 120 = 9
4. The aspect ratio is 16:9.

This is why many HD and 4K formats are described as 16:9, even though they have different pixel counts.

Using aspect ratios to resize without distortion

Once you know the aspect ratio, you can generate new dimensions that keep the same shape by multiplying both sides of the ratio by the same factor. This is true whether you are scaling up to a large display or down to a small thumbnail.

For example, consider a 16:9 ratio. Some proportional sizes include:

• 16 × 9 (abstract units)
• 1600 × 900 pixels (factor 100)
• 1920 × 1080 pixels (factor 120)
• 3840 × 2160 pixels (factor 240)

In each case, the width divided by the height is the same, so the image or video will look identical in shape. Only the resolution or physical size changes.

Worked example: scaling a design

Imagine you designed a slide at 1280 × 720 pixels (16:9), but your display requires 2560 × 1440 pixels. To check whether the new size matches, divide the target width and height by the original:

• 2560 ÷ 1280 = 2
• 1440 ÷ 720 = 2

Both dimensions are exactly doubled, so the aspect ratio remains 16:9. You will not see stretching or pillarboxing.

Common aspect ratios and typical uses

Many devices and platforms favor a small set of aspect ratios. Knowing them helps you plan your projects so fewer adjustments are needed later.

These examples are not strict rules—platforms can support multiple ratios—but they provide a helpful starting point when planning content.

Interpreting your calculator results

After you enter width and height, the calculator typically returns:

• The simplified ratio, such as 16:9 or 3:2, based on your exact dimensions.
• The decimal ratio (width ÷ height), which shows how wide the content is relative to its height.
• Optionally, sample dimensions that share the same ratio, which you can use as alternate sizes.

You can compare the simplified ratio to the common values above to understand how your content will behave on different screens:

• If the result is very close to 16:9, it should fill most modern video players without letterboxing.
• If the result is closer to 9:16, it will be better suited to vertical mobile viewing.
• If the ratio is unusual (for example, 7:5), you may need to add padding or crop strategically for standard layouts.

Practical tips: web, print, and social media

Web and UI design

On the web, aspect ratio affects how images and video fit into responsive layouts. Designers often:

• Choose a consistent ratio for hero banners (commonly wide, such as 16:9 or 21:9).
• Use fixed ratios for cards or thumbnails so image grids line up neatly.
• Test how media behaves when containers change width on different screens.

By matching your assets to the container ratio, you reduce the chance of unexpected cropping or whitespace.

Print layouts

Print sizes are usually described by their physical dimensions (such as 8 × 10 inches or A4), but they still have aspect ratios. If your photo does not match the paper ratio, then either whitespace or cropping is required.

For example:

• An 8 × 10 inch print has a 4:5 ratio.
• A 6 × 4 inch print has a 3:2 ratio.

If your camera produces 3:2 images and you print at 4:5 without adjustment, part of the image must be trimmed. Checking the ratio ahead of time helps you compose your shot with safe margins.

Social and mobile video

Social platforms favor vertical and square formats for mobile viewing. Typical choices include:

• 1:1 for feed posts that should stand out in both desktop and mobile views.
• 4:5 or similar vertical formats to occupy more vertical space without being fully fullscreen.
• 9:16 for stories, reels, and shorts that fill the phone screen.

Using the calculator, you can confirm whether your exported video fits the expected ratio before uploading, reducing the need for re-exports or last-minute crops.

Limitations, assumptions, and notes

This aspect ratio calculator is designed to be simple and focused. To use it correctly, keep these points in mind:

• Units do not matter for the ratio. You can enter pixels, inches, millimeters, or any other length unit as long as both inputs use the same unit. The ratio itself is unitless.
• The tool does not modify files. It only calculates the relationship between width and height. It does not open, resize, crop, or compress images or video.
• No DPI or file size handling. Dots per inch (DPI), resolution for printing, and file size (megabytes) are outside the scope of this calculator. Those are determined by your editing software and export settings.
• Rectangular content is assumed. The math assumes standard rectangular media. It does not account for panoramic stitching, circular crops, or irregular shapes.
• Rounding may occur. When dimensions are large or include decimals, the simplified ratio may be rounded to nearby whole numbers that are visually indistinguishable.
• Platform guidelines can change. While common aspect ratios are fairly stable, specific platform recommendations (for example, exact pixel sizes or safe margins for overlays) may evolve over time. Always check current documentation when preparing critical assets.

Within these limits, the calculator gives you a fast, reliable way to understand and control the shape of your media across different sizes and formats.