WorldCalcs

Aspect Ratio Calculator

Find the aspect ratio of any width and height, or resize while keeping the same ratio.

Reviewed by the WorldCalcs team · Methodology · Last reviewed: June 2026

Simplified ratio

16:9

Decimal ratio (W ÷ H)

1.7778

What is an aspect ratio?

An aspect ratio is the relationship between the width and the height of a rectangle, written as W:H. It describes the shape of an image, video or screen, not its size. A 1280×720 photo and a 1920×1080 photo are very different in pixel count, but they're the same shape — both are 16:9.

Aspect ratios are why a 16:9 video looks right on a widescreen TV but has black bars on a 4:3 old-style screen. The content has to be stretched, cropped or letterboxed when the shape of the source doesn't match the shape of the display.

How simplification works

To find the ratio of any width and height, divide both numbers by their greatest common divisor (gcd). For 1920×1080, gcd(1920, 1080) is 120, so the ratio is 1920÷120 : 1080÷120 = 16:9. For 1280×1024, gcd is 256, so the ratio is 5:4. Mode A above does this gcd reduction for you and also reports the decimal ratio (width ÷ height) for cases that don't reduce to small numbers — for example 2560×1080 reduces to 64:27, which most people just call 21:9.

How resizing keeps the ratio

To resize without distortion you scale both dimensions by the same factor. If you know one new side and the target ratio, solve for the other: missing height = known width × ratio H ÷ ratio W, and missing width = known height × ratio W ÷ ratio H. For a 16:9 image at 1280 wide, the height is 1280 × 9 ÷ 16 = 720. Mode B above does the arithmetic and includes presets for the common ratios (16:9, 4:3, 21:9, 1:1, 3:2, 9:16).

Examples

  • 1920×1080 → 16:9 (decimal 1.7778)
  • 1280×1024 → 5:4
  • 800×600 → 4:3
  • 2560×1080 → 64:27 (commonly called 21:9)
  • Ratio 16:9 at width 1920 → height 1080
  • Ratio 4:3 at width 1024 → height 768

For working with raw ratios as fractions, see the ratio calculator. For converting an area in different units, the square footage calculator covers length × width in feet and meters. To scale prices or quantities by a percentage instead of a ratio, use the percentage calculator.

All calculations happen in your browser. Nothing is sent, stored, or tracked.

Results are estimates and may contain errors — for general information only, not professional advice. Always verify before relying on them. Disclaimer

How to use

Find the ratio: enter width and height to get the simplified ratio (e.g. 16:9) plus the decimal ratio.

Resize: pick a preset ratio (or type your own as W:H), enter one known dimension, and the calculator solves the other side so the proportions stay the same.

Frequently asked questions

What is 16:9?+

16:9 is the standard widescreen aspect ratio: for every 16 units of width there are 9 units of height. It's the native shape of almost every modern TV, laptop and computer monitor, and the default video size on YouTube. Common 16:9 resolutions include 1280×720 (HD), 1920×1080 (Full HD) and 3840×2160 (4K UHD).

What aspect ratio is 1920×1080?+

1920×1080 simplifies to 16:9. Divide both numbers by their greatest common divisor — gcd(1920, 1080) = 120 — and you get 16 and 9. Any image or video that's 1920 wide and 1080 tall is a true 16:9 frame.

How do I resize an image without distortion?+

Keep the same ratio of width to height. If the original is 1920×1080 (16:9) and you want it 1280 wide, the new height is 1280 × 9 ÷ 16 = 720. Use Mode B above: pick the ratio, type the known side, and the other side falls out automatically.

What is 4:3 aspect ratio?+

4:3 is the classic standard-definition shape: 4 units wide for every 3 units tall. Old CRT televisions, early digital cameras and iPads use 4:3. Common 4:3 resolutions include 640×480, 800×600, 1024×768 and 1600×1200.

What is 21:9?+

21:9 is the ultrawide cinematic aspect ratio used by ultrawide monitors and modern movies. The exact shape varies — 2560×1080 is actually 64:27 and 3440×1440 is 43:18 — but both are marketed as 21:9 because they're close to that ratio and noticeably wider than 16:9.

How do I find the aspect ratio of an image?+

Take the width and height in pixels, find their greatest common divisor (gcd), and divide both numbers by it. For 1280×1024, gcd is 256, so the ratio is 5:4. This calculator does the gcd reduction for you and also shows the decimal ratio (width ÷ height) for ratios that don't simplify to small whole numbers.

What aspect ratio should I use for YouTube or Instagram?+

YouTube standard videos are 16:9, YouTube Shorts and TikTok are 9:16 vertical, and Instagram posts can be 1:1 (square), 4:5 (portrait) or 1.91:1 (landscape). Instagram Reels and Stories are 9:16. Pick the target ratio in Mode B and the calculator gives you the correct export dimensions.

What's the difference between the golden ratio and an aspect ratio?+

An aspect ratio is just the width-to-height shape of a rectangle, like 16:9 or 4:3. The golden ratio is a specific mathematical ratio (about 1.618:1) that appears in design and nature. You can have an image with a golden-ratio aspect — roughly 1.618:1 — but most screens and cameras use 16:9, 4:3, 3:2 or 1:1 instead.

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