Aspect Ratio Calculator

An aspect ratio is the proportional relationship between the width and height of a rectangle, written as two numbers separated by a colon, such as 16:9. This calculator lets you enter known dimensions or a target ratio and instantly find the missing value, so an image, video frame, or container scales without stretching or cropping. It keeps the shape constant while the size changes.

How to use it

1. Enter the original width and height, or pick a standard ratio like 16:9, 4:3, 1:1, or 21:9.
2. Type the one new dimension you already know, for example a target width of 1280.
3. Read the calculated value for the remaining dimension that preserves the same ratio.
4. Swap which field you fill to solve for either width or height as needed.
5. Copy the result into your editor, CSS, or export settings.

How scaling while keeping the ratio works

The ratio is simply width divided by height. To resize without distortion, both dimensions must be multiplied by the same factor. If a 1920x1080 frame (16:9) is scaled to a width of 1280, the factor is 1280 divided by 1920, which is 0.6667; multiplying 1080 by that factor gives 720. The reverse works too: known height times the ratio gives the width. The calculator handles this arithmetic and reduces ratios to their simplest form using the greatest common divisor, so 1920:1080 displays as 16:9.

Ratio	Shape	Common use
16:9	Widescreen	Video, monitors, YouTube
4:3	Standard	Older displays, some photos
1:1	Square	Avatars, social posts
21:9	Ultrawide	Cinematic video, monitors

FAQ

What does 16:9 actually mean?

It means that for every 16 units of width there are 9 units of height. The numbers are a proportion, not pixels, so any size that keeps that 16-to-9 relationship looks identical in shape, whether it is 1280x720 or 3840x2160.

How do I keep the ratio when resizing an image?

Decide one target dimension, then let the calculator find the other. Setting both freely will distort the picture. Many editing tools also offer a lock or chain icon that applies this same proportional math automatically.

Can I use this for responsive CSS?

Yes. Modern CSS supports the aspect-ratio property, where you write a value like 16 / 9 on a container so it reserves the correct height for its width. The calculated ratio from this tool maps directly to that value.

Why is my ratio shown as a smaller pair of numbers?

Ratios are reduced to their simplest equivalent. Dividing 1920 and 1080 by their greatest common divisor, 120, yields 16 and 9, which is easier to read and compare against standard formats.