How do I calculate an aspect ratio from pixels?

Enter your pixel width and height into this calculator. It will automatically find the greatest common divisor (GCD) of the two numbers and reduce them to the simplest ratio — for example, 1920×1080 becomes 16:9.

How do I resize an image while keeping the aspect ratio?

Enter your original width and height first to lock in the ratio. Then enter only your desired new width or new height in the scaling section — the calculator will automatically compute the other dimension to maintain perfect proportions.

What aspect ratio should I use for YouTube videos?

YouTube recommends 16:9 (widescreen) for standard videos. The recommended resolution is 1920×1080 pixels (Full HD) or 3840×2160 (4K). Shorts use 9:16 vertical format.

What is the difference between 16:9 and 4:3?

16:9 is a widescreen format used by modern TVs, YouTube, and HD video. It's wider relative to its height. 4:3 is the older 'fullscreen' format used by traditional televisions and early computer monitors — more square in shape. Most modern content uses 16:9.

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Calculators & Converters

Free Aspect Ratio Calculator

Q: What is an aspect ratio?

An aspect ratio is the proportional relationship between a display's or image's width and height. It's expressed as two numbers separated by a colon — for example, 16:9 means the width is 16 units for every 9 units of height. It describes shape, not actual size.

Calculate, convert, and scale aspect ratios instantly. Perfect for designers, video editors, and photographers who need pixel-perfect proportions.

Step 1 — Enter original dimensions

Width (px)

Height (px)

Step 2 — Scale to new dimensions Keeps ratio locked

New Width (px)

New Height (px)

Common Aspect Ratios

Click any row to load those dimensions into the calculator.

Ratio	Decimal	Example Sizes	Common Uses
16:9	1.78	1920×1080, 3840×2160	YouTube HD/4K TV Widescreen Zoom
4:3	1.33	1024×768, 1600×1200	Traditional TV Old monitors iPad
1:1	1.00	1080×1080, 500×500	Instagram Posts Profile Photos Thumbnails
21:9	2.33	2560×1080, 3440×1440	Ultrawide Monitors Cinema Cinematic Video
9:16	0.56	1080×1920, 720×1280	TikTok Instagram Stories YouTube Shorts
3:2	1.50	3000×2000, 1500×1000	DSLR / Mirrorless Photography Print

How to Use This Calculator

Enter your original width and height in pixels. The aspect ratio will calculate instantly.
To scale to a new size, enter either a new width or a new height — the other dimension is calculated automatically to preserve the ratio.
Use the Swap button to flip width ↔ height (useful for switching between landscape and portrait).
Click any row in the Common Ratios table to instantly load standard dimensions for quick reference.

What is an Aspect Ratio?

An aspect ratio defines the proportional relationship between a display's width and height. It's expressed as two integers separated by a colon — for example, 16:9 means 16 units wide for every 9 units tall. The numbers describe shape, not absolute size: a 3840×2160 screen and a 1920×1080 screen both have a 16:9 aspect ratio.

Aspect ratios are fundamental in photography, video production, web design, and print. When you resize an image or video without locking the aspect ratio, the result looks stretched or squished. This calculator ensures every resize stays perfectly proportional.

The ratio is calculated by finding the Greatest Common Divisor (GCD) of the width and height, then dividing both numbers by it. For example: 1920 and 1080 share a GCD of 120, so 1920÷120 = 16 and 1080÷120 = 9 — yielding 16:9.

Frequently Asked Questions

An aspect ratio is the proportional relationship between an image's width and height, expressed as two numbers separated by a colon (e.g., 16:9 or 4:3). It describes the shape of a frame — not its actual size. The same ratio can apply to a small icon or a billboard.
Enter your width and height (in pixels) into the fields above. The calculator finds the Greatest Common Divisor (GCD) of the two values and divides both by it to produce the simplest ratio. For example, 1920×1080 → GCD is 120 → 16:9.
Enter your original width and height to lock in the ratio. Then use the "Scale to new dimensions" section — enter only your desired new width or new height. The calculator automatically computes the missing value so your proportions stay identical.
YouTube recommends 16:9 for standard videos. The ideal resolution is 1920×1080 (Full HD) or 3840×2160 (4K). For YouTube Shorts, use the vertical 9:16 format (1080×1920). Videos with other ratios get letterboxed or pillarboxed automatically.
16:9 is the modern widescreen standard used by HD/4K TVs, YouTube, and most digital content — it's wider relative to its height. 4:3 is the classic "fullscreen" format from traditional televisions and early computer monitors, producing a more square image. Most cameras, screens, and platforms today default to 16:9.