Aspect Ratio Calculator

What the Aspect Ratio Calculator Does

This tool finds the aspect ratio of an image, video, or screen from its width and height, and it resizes those dimensions proportionally so nothing gets stretched or squashed. Enter a current width and height to see the ratio (for example 16:9), or enter a new width to get the matching new height automatically.

It's useful for photographers cropping to print sizes, video editors targeting 16:9 or 9:16, web designers fitting images into layouts, and anyone scaling artwork without distortion.

How It Works: The Aspect Ratio Formula

Aspect ratio is simply the relationship between width and height. The calculator uses two short formulas:

To keep an image undistorted when you change its size, the width-to-height relationship must stay the same. That is exactly what the second formula guarantees.

• Ratio = width ÷ height
• New height = new width × (height ÷ width)
• New width = new height × (width ÷ height)

Worked Example

Say you have a photo that is 1920 × 1080 pixels and you need it to be 1280 pixels wide for a webpage.

First, the ratio: 1920 ÷ 1080 = 1.777..., which is the familiar 16:9. Now solve for the new height: new height = 1280 × (1080 ÷ 1920) = 1280 × 0.5625 = 720. So 1280 × 720 keeps the exact same proportions as 1920 × 1080. Going the other way, if you fixed the height at 720, new width = 720 × (1920 ÷ 1080) = 720 × 1.777... = 1280.

Reading Common Ratios

Ratios are usually written as two whole numbers separated by a colon. You get them by dividing both dimensions by their greatest common divisor. For 1920 and 1080 that divisor is 120, giving 16:9.

Frequently used ratios include:

• 16:9 — standard widescreen video and most monitors
• 4:3 — older displays, many tablets, and some cameras
• 1:1 — square images for social media posts
• 3:2 — common DSLR photo and 4×6 inch prints
• 9:16 — vertical video for phones and short-form clips

Tips and Common Mistakes

The most common error is changing width and height by different percentages, which stretches the image. Always let one dimension drive the other through the formula. Another pitfall is confusing aspect ratio with resolution: 1280 × 720 and 1920 × 1080 share the 16:9 ratio but hold very different pixel counts and detail.

Keep these points in mind:

• Resized values may not be whole pixels (for example 0.5 px). Round to the nearest integer, which can shift the ratio by a hair.
• Cropping changes the ratio; scaling does not. Decide which you actually need.
• Enlarging beyond the original size keeps proportions but cannot add real detail, so the result looks softer.
• When fitting into a fixed box, resize so the larger side meets the limit, then check the other side still fits.