Aspect Ratio Calculator

Lock a ratio like 16:9 and solve a missing width or height, or enter any width × height to reduce it to a clean, lowest-terms ratio.

🔒 Runs entirely in your browser — nothing is sent anywhere

What do you want to do?

The proportion you want to keep between width and height.

Known dimension

Fill in the one dimension you know (in pixels or any unit) and we'll solve the other.

Leave blank to solve for width.

Leave blank to solve for height.

How this works

Aspect ratio is just the proportion of width to height. This tool works it out two ways — every calculation runs instantly on your device.

1

Pick a ratio

Choose a preset like 16:9, 4:3 or 21:9, or type your own custom W : H. This is the shape you want to preserve.

2

Solve a dimension

Enter one side — width or height — and we scale the other by the ratio so the proportions stay exactly the same.

3

Or find the ratio

Give any width × height and we divide both by their greatest common divisor to reveal the clean ratio, like 1920×1080 → 16:9.

Common aspect ratios

RatioDecimalTypical use
16 : 91.778HD & 4K video, monitors, YouTube
4 : 31.333Classic TV, older displays, some tablets
21 : 92.333Ultrawide monitors, cinematic film
1 : 11.000Square social posts, profile pictures
3 : 21.500DSLR photos, 4×6 prints
9 : 160.563Vertical video, Reels, Stories

Need to actually change an image's size or shape? Resize within the same ratio with the image resizer, or trim to a new ratio without stretching using the image cropper. Both run entirely in your browser too.

🔒

Private by design. Every number stays on your device. Nothing you type is uploaded, stored or shared.

Frequently Asked Questions

How do I find the missing width or height for a ratio? ▼
Pick a target ratio (or type a custom one), enter the one dimension you already know, and the calculator instantly works out the other side. For example, with a 16:9 ratio and a width of 1280 px, the height comes out to 720 px.
How is a resolution like 1920×1080 simplified to 16:9? ▼
We take the greatest common divisor (GCD) of the two numbers and divide both by it. For 1920 and 1080 the GCD is 120, so 1920÷120 : 1080÷120 gives 16 : 9 — the lowest-terms whole-number ratio.
What are the most common aspect ratios? ▼
16:9 is standard for HD/4K video and most monitors, 4:3 is the classic television and older display ratio, 21:9 is ultrawide/cinematic, 1:1 is square (social posts), and 3:2 is common for DSLR photos and prints.
Can I use decimal dimensions? ▼
Yes. You can enter decimals such as 12.5, and the calculator handles them correctly when solving a side. When reducing a width × height to a ratio it scales decimals up to whole numbers before applying the GCD, so the result stays clean.
Does resizing to a new ratio distort my image? ▼
Changing an image to a different aspect ratio either stretches it or crops away part of it. To keep proportions, resize within the same ratio using our image resizer, or trim to a new shape without stretching using the image cropper.
Is my data sent anywhere? ▼
No. Every calculation runs entirely in your browser with JavaScript. Nothing you type is uploaded, stored or shared — the tool works even offline once the page has loaded.

Free to use · works entirely in your browser · no account needed.

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