How do I calculate the aspect ratio from width and height?

Divide the width and height by their Greatest Common Divisor (GCD). For example, 1920×1080: GCD is 120, so 1920÷120 = 16 and 1080÷120 = 9 — giving 16:9. The CalcMeter aspect ratio calculator does this automatically the moment you type your dimensions.

What aspect ratio should I use for YouTube videos?

YouTube recommends 16:9 (1920×1080 for 1080p, 3840×2160 for 4K). YouTube Shorts and vertical content should use 9:16 (1080×1920). Thumbnails are 1280×720 (16:9).

What aspect ratio does Instagram use?

Instagram supports multiple aspect ratios: 1:1 (square, 1080×1080) for feed posts, 4:5 (portrait, 1080×1350) for portrait posts, 1.91:1 (landscape, 1080×566) for landscape posts, and 9:16 (1080×1920) for Reels and Stories.

How do I scale image dimensions while keeping the aspect ratio?

Use the Scale Dimensions mode: enter your original width and height, then enter the new width or height you want. The calculator finds the missing dimension using the formula: new_height = (new_width / original_width) × original_height.

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

16:9 (widescreen) has a decimal ratio of ~1.78 and is used by modern TVs, YouTube, and most video content. 4:3 (standard) has a decimal ratio of ~1.33 and was used by older TVs and monitors. At the same height, a 16:9 frame is about 33% wider than a 4:3 frame.

Aspect Ratio Calculator — Find, Scale & Convert Ratios for Video, Photo & Social Media

Enter width & height in pixels

Width (px)

Height (px)

Enter any pixel dimensions — e.g. 1920 × 1080 — and get the simplified ratio, decimal, megapixels, orientation, and the closest standard format.

Original dimensions

Original Width (px)

Original Height (px)

Enter one new dimension — the other is calculated

New Width (px)

New Height (px)

Enter original dimensions, then type either the new width or height — the missing value is calculated automatically.

Enter the ratio

Ratio Width

Ratio Height

Known dimension

Width (px)

Enter a ratio like 16:9, choose whether you know the width or height, type the value, and get the missing dimension.

Presets

Visual Preview

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Simplified Ratio

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Reduced to lowest whole numbers

Decimal Ratio

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Width ÷ Height

Megapixels

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Total pixel count

Orientation

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Crop to Common Ratios — center crop from your —

Ratio	Crop Dimensions	Trimmed

What Is an Aspect Ratio?

An aspect ratio is the proportional relationship between a frame's width and height, expressed as two numbers separated by a colon — like 16:9 or 4:3. It describes the shape of an image or video without specifying actual pixel dimensions. A 1280×720 video and a 3840×2160 video both have a 16:9 aspect ratio — they are the same shape, just different resolutions.

Aspect ratios are used everywhere: video production, photography, social media uploads, print design, and screen manufacturing. Getting the ratio wrong causes black bars (letterboxing or pillarboxing), cropping, or distorted images.

Most Common Aspect Ratios & Where They're Used

16:9

HD Widescreen

YouTube, Netflix, TVs, most monitors, Zoom. The dominant format since 2009.

9:16

Vertical / Stories

Instagram Reels, TikTok, YouTube Shorts, Snapchat. 16:9 rotated 90°.

4:3

Classic Standard

Old TVs, iPads, Micro 4/3 cameras. Still common in education & video conferencing.

1:1

Square

Instagram feed posts, profile photos, album art, favicon grids.

21:9

Ultrawide

Ultrawide monitors, cinematic gaming, wide-format video.

3:2

DSLR / APS-C

Full-frame & APS-C cameras (Canon, Nikon, Sony). Also 4×6 photo prints.

4:5

IG Portrait

Instagram portrait posts. The tallest ratio Instagram allows in-feed without cropping.

2.39:1

Anamorphic Cinema

Cinematic widescreen films. Nolan's films, most Hollywood blockbusters.

How to Calculate Aspect Ratio from Pixels

The formula uses the Greatest Common Divisor (GCD) of width and height:

function gcd(a, b) { return b === 0 ? a : gcd(b, a % b); } // Example: 1920 × 1080 const g = gcd(1920, 1080); // → 120 const ratio = `${1920 / g}:${1080 / g}`; // → "16:9"

Divide both dimensions by their GCD. For 1920×1080: GCD is 120, so 1920÷120 = 16 and 1080÷120 = 9 → 16:9. For 2560×1440: GCD is 80 → 32:18 → further reduced to 16:9.

How to Scale Image Dimensions While Keeping Aspect Ratio

To resize an image proportionally, use cross-multiplication:

// Scale to a new width new_height = (new_width / original_width) × original_height // Example: 1920×1080 image → 800px wide new_height = (800 / 1920) × 1080 = 450px

In CSS you can preserve aspect ratio automatically with width: 100%; height: auto; on an <img> tag, or use the aspect-ratio property on a container.

Aspect Ratios for Social Media Platforms (2025)

YouTube

Standard videos: 16:9 (1920×1080 for 1080p, 3840×2160 for 4K). YouTube Shorts: 9:16 (1080×1920). Thumbnails: 1280×720 (16:9).

Instagram

Square posts: 1:1 (1080×1080). Portrait posts: 4:5 (1080×1350 — maximizes screen real estate in the feed). Landscape posts: 1.91:1 (1080×566). Reels & Stories: 9:16 (1080×1920).

TikTok

Standard vertical: 9:16 (1080×1920). Landscape: 16:9. Square: 1:1.

Twitter / X

Single image: up to 16:9, optimal 1600×900. Profile header: 1500×500 (3:1).

Post images: 1.91:1 to 1:1. Cover photo: 1584×396 (4:1).

Letterboxing vs. Pillarboxing

Letterboxing adds horizontal black bars (top and bottom) when a wide-format video is shown in a narrow-format container. For example, a 16:9 film displayed in a 4:3 TV frame gets black bars on top and bottom.

Pillarboxing adds vertical black bars (left and right) when a narrow-format source is displayed in a wider frame. For example, a 4:3 video in a 16:9 frame gets bars on the sides.

Use the Scale Dimensions mode above to check the exact pixel dimensions of your content and crop area before exporting.

Aspect Ratio in Photography

Most DSLR and mirrorless cameras (Canon, Nikon, Sony full-frame and APS-C) shoot in 3:2. Micro Four Thirds (Panasonic, Olympus) shoot in 4:3. Medium format cameras like Hasselblad use 4:3 or 1:1. Understanding your camera's native ratio helps you plan compositions that won't be cropped when printed to standard paper sizes like 4×6 (3:2) or 8×10 (4:5).

Aspect Ratio Calculator