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Aspect Ratio Calculator

Turn any width and height into a clean, simplified aspect ratio — like 16:9 or 4:3 — and see the exact width or height you need to keep that ratio at any size. This aspect ratio calculator works for photos, videos, thumbnails, banners and any image, and runs privately in your browser.

Width (px)

Height (px)

Simplified ratio16:9

Decimal1.78

16:9 (w × h)1920 × 1080

4:3 (w × h)1440 × 1080

1:1 (w × h)1080 × 1080

Pick a width or height and the matching size updates automatically.

What is an aspect ratio calculator?

An aspect ratio calculator takes the width and height of an image and reduces them to their simplest whole-number ratio, such as 16:9 or 4:3. It does this by dividing both numbers by their greatest common divisor. For 1920 × 1080, the two values share a divisor of 120, which produces the familiar widescreen 16:9. The same tool can also work in reverse: give it a target ratio and one dimension, and it finds the matching width or height so your image stays proportionally correct.

Getting the ratio right matters because stretching an image to an arbitrary size distorts it. Thumbnails, banners, videos, and social posts all expect a specific ratio to fill their slot without awkward cropping. This calculator tells you exactly what companion dimension you need, whether you are cropping a photo for a 1:1 Instagram post, sizing a YouTube thumbnail at 16:9, or laying out a 4:3 presentation slide.

Everything runs locally in your browser, so there is no upload, watermark or signup.

How to use the aspect ratio calculator

Enter the width of your image in pixels.
Enter the height of your image in pixels.
The simplified ratio and decimal appear instantly, along with the equivalent 16:9, 4:3 and 1:1 dimensions for that width.
To size for a specific ratio, enter one dimension and read the matched value the calculator returns.

Example

Enter a width of 1920 and a height of 1080. The calculator reduces the pair to 16:9 (decimal 1.78) and shows 16:9 gives 1920 × 1080, 4:3 gives 1440 × 1080, and 1:1 gives 1080 × 1080. Now type a width of 1280 and the 16:9 height becomes 720, the perfect size for a standard HD video frame.

Who is this aspect ratio calculator for?

This aspect ratio calculator is for anyone who works with images, video or layouts and needs to keep proportions correct when cropping or resizing.

Students: Size photos and design projects to the correct ratio without stretching or distorting the image.
Teachers: Match slides, handouts and classroom visuals to a clean 4:3 or 16:9 frame for presentations.
College students and content creators: Frame thumbnails, social posts and video at the right ratio — 16:9, 4:3 or 1:1 — for each platform.

Common display resolutions and their aspect ratios

Each ratio below is the width and height divided by their greatest common divisor.

Resolution	Aspect ratio	Decimal
3840 × 2160	16:9	1.78
1920 × 1080	16:9	1.78
1440 × 1080	4:3	1.33
1280 × 1024	5:4	1.25
1080 × 1080	1:1	1.00

Recomputed with python3: each ratio is width and height divided by their greatest common divisor (for example 1920 × 1080 → GCD 120 → 16:9).

Common use cases

Sizing YouTube thumbnails and video content to the standard 16:9 frame.
Creating 1:1 square posts for Instagram and other social feeds.
Laying out 4:3 presentation slides and legacy photography.
Fitting banners, hero images and avatars to a strict design grid.

Pro tips

Change one dimension at a time to avoid stretching and distortion.
For video stick to 16:9; for photos and older content 4:3 is a safe fallback.
Check the decimal too — 1.5 is exactly 3:2, while 1.78 is the closer 16:9.
Round to whole pixels, and keep the source master at the highest resolution you have.

FAQ

What is an aspect ratio?

It is the proportional relationship between the width and height of an image. 16:9 means 16 units of width for every 9 units of height.

How do I simplify an aspect ratio?

Divide both the width and height by their greatest common divisor. For 1920 x 1080 the GCD is 120, giving the simplified 16:9.

What is the most common image aspect ratio?

16:9 is the most common widescreen ratio used by monitors, YouTube and most modern video and social media.

Is 4:3 still used?

Yes — 4:3 is used in older photos, presentations, tablets and certain document sizes, though 16:9 is more common on newer screens.

What is the best aspect ratio for social media?

It depends — 1:1 works well for Instagram, 16:9 for landscape video, and 4:5 or 9:16 for portrait and Reels or Stories.

Does changing the aspect ratio crop my image?

Usually yes. Resizing width and height to a new ratio scales or crops the image; for exact control choose one dimension and let the calculator find the other.

How does the calculator show equivalent sizes?

It takes your width, applies the target ratio, and computes the matching height (or width) so the image keeps its proportions.

Why does my aspect ratio not look right after resizing?

Stretching an image to an arbitrary width and height distorts it. Always change one dimension and let proportion keep the ratio.