What is an aspect ratio?

It is the reduced width-to-height proportion of an image, video, or screen. 1920×1080 and 1280×720 share the same 16:9 aspect ratio even though the pixel counts differ.

How do I calculate aspect ratio?

Divide width and height by their greatest common divisor. 1920÷120 and 1080÷120 both become 16 and 9, so the ratio is 16:9. Simplify mode does this automatically and also shows the decimal (≈1.7778).

How do I find the missing dimension?

In Scale mode, enter the target ratio, lock the side you know, and read the other. Example: 16:9 with width 1920 → height 1080; 9:16 with width 1080 → height 1920.

What are common 16:9 resolutions?

720p is 1280×720, 1080p is 1920×1080, QHD is 2560×1440, and 4K UHD is 3840×2160. The common-size chips on this page load matching widths for the active ratio.

How do I use this with CSS?

Copy the CSS output, for example `aspect-ratio: 16 / 9;`, onto a container so it keeps the ratio while width is fluid. Pair with object-fit when the media inside must crop.

Which presets are included?

16:9, 9:16, 4:3, 3:2, 1:1, 21:9, 2:1, 5:4, 3:4, and 2:3 - common for video, photo, print, and social formats.

Does this upload my dimensions?

No. The Aspect Ratio Calculator runs entirely in your browser. Width and height values never leave this tab.

Calculator Tools

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Aspect Ratio Calculator

Enter a size to simplify the ratio, or lock one side and scale the other to 16:9, 9:16, 4:3, and more.

Ratio math runs in your browser. Nothing is uploaded.

Common ratios

Width

Height

Aspect ratio

16:9

Decimal

1.7778

Size

1,920 × 1,080

CSS

aspect-ratio: 16 / 9;

Common pixel sizes

About Aspect Ratio Calculator

An aspect ratio is the proportional relationship between width and height - written as W:H after reducing by their greatest common divisor (1920×1080 → 16:9). Use Simplify mode to read the reduced ratio, decimal, preview box, and CSS `aspect-ratio` value. Use Scale mode to lock width or height and solve the other side for 16:9, 9:16, 4:3, 1:1, 21:9, and more. Common pixel chips jump to sizes like 1920×1080. Pair it with the Image Resizer when you need a downloaded crop, or Pixels to Inches for print size.

How to Use Aspect Ratio Calculator

Simplify mode: enter width and height to get the reduced ratio, decimal, preview, and CSS snippet.
Scale mode: set ratio parts (or tap a preset), lock width or height, and read the matching other side.
Use presets (16:9, 9:16, 4:3, 3:2, 1:1, 21:9, and more) for common photo and video formats.
Click a common pixel size to load it, then copy the summary or `aspect-ratio: W / H;` CSS.

Aspect Ratio Calculator Formula

Reduce width and height by gcd(W, H) to get the aspect ratio. Missing side: height = width × (ratioH ÷ ratioW), or width = height × (ratioW ÷ ratioH). CSS: aspect-ratio: W / H. Example: 1920×1080 → divide by 120 → 16:9.

Aspect Ratio Calculator Examples

Full HD 16:9

1920×1080 simplifies to 16:9. CSS: aspect-ratio: 16 / 9;

Find height from width

Lock width 1280 on 16:9 → height 720. Lock width 3840 → height 2160 (4K UHD).

Vertical social 9:16

Lock width 1080 on 9:16 → height 1920 for Stories / Reels-style frames.

4:3 classic

1024×768 or lock height 768 on 4:3 → width 1024.

Square crop

Equal sides (for example 1080×1080) simplify to 1:1 for avatars and product tiles.

Common Use Cases

Crop photos and thumbnails to a known ratio
Size YouTube, Twitch, or social video frames (16:9 / 9:16)
Generate CSS aspect-ratio values for responsive UI
Pick common pixel dimensions for a target ratio
Check whether a resolution matches 4:3, 3:2, or ultrawide 21:9
Keep proportions when scaling a design mockup

Frequently Asked Questions about Aspect Ratio Calculator

What is an aspect ratio?: It is the reduced width-to-height proportion of an image, video, or screen. 1920×1080 and 1280×720 share the same 16:9 aspect ratio even though the pixel counts differ.
How do I calculate aspect ratio?: Divide width and height by their greatest common divisor. 1920÷120 and 1080÷120 both become 16 and 9, so the ratio is 16:9. Simplify mode does this automatically and also shows the decimal (≈1.7778).
How do I find the missing dimension?: In Scale mode, enter the target ratio, lock the side you know, and read the other. Example: 16:9 with width 1920 → height 1080; 9:16 with width 1080 → height 1920.
What are common 16:9 resolutions?: 720p is 1280×720, 1080p is 1920×1080, QHD is 2560×1440, and 4K UHD is 3840×2160. The common-size chips on this page load matching widths for the active ratio.
How do I use this with CSS?: Copy the CSS output, for example `aspect-ratio: 16 / 9;`, onto a container so it keeps the ratio while width is fluid. Pair with object-fit when the media inside must crop.
Which presets are included?: 16:9, 9:16, 4:3, 3:2, 1:1, 21:9, 2:1, 5:4, 3:4, and 2:3 - common for video, photo, print, and social formats.
Does this upload my dimensions?: No. The Aspect Ratio Calculator runs entirely in your browser. Width and height values never leave this tab.

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