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Aspect Ratio Calculator

Calculate the aspect ratio of any resolution instantly. Enter width and height to get the simplified ratio (16:9, 4:3, 1:1…), decimal value, and closest common format. Free, runs in your browser.

Presets:

Width (px)

×

Height (px)

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Aspect ratio is the proportional relationship between the width and height of a rectangular shape, expressed as two numbers separated by a colon (e.g., 16:9 or 4:3). It describes the shape of an image, video frame, screen, or print without specifying the actual dimensions — a 1920×1080 video and a 3840×2160 video both have a 16:9 aspect ratio.

Maintaining aspect ratio during resizing is critical for avoiding distorted (stretched or squished) images and videos. Web developers, graphic designers, and video editors constantly encounter aspect ratio calculations when resizing images to fit containers, exporting video at different resolutions, cropping to standard formats, or calculating the height of a responsive element given only its width.

This tool calculates the simplified aspect ratio from any width and height using the GCD (Greatest Common Divisor) algorithm, and also shows the decimal ratio, the inverse (height:width), and the closest common standard ratio (16:9, 4:3, 1:1, 21:9, etc.). Enter any two dimensions and all derived values appear instantly.

Common Use Cases

Resizing images without distortion

When you have a 1200×675 image and need a version that is exactly 400 pixels wide, the correct height is (675 / 1200) × 400 = 225 pixels. Deviating from this ratio stretches or squishes the image. The calculator confirms the ratio is 16:9 and computes the correct proportional dimension for any target size, saving manual arithmetic.

Designing responsive CSS elements

Embedding a 16:9 video in a responsive layout requires a padding-bottom trick: if the container width is 100%, padding-bottom should be 56.25% (9/16 × 100). For non-standard ratios like 2.39:1 (cinemascope), calculating the exact percentage requires knowing the decimal ratio — the tool provides this directly.

Verifying video export settings

When exporting footage from DaVinci Resolve, Premiere Pro, or FFmpeg, you must specify the output resolution. Checking that 2560×1440 preserves the same 16:9 ratio as the source footage prevents letterboxing or cropping surprises. The calculator instantly confirms whether a proposed export resolution maintains the source aspect ratio.

Cropping images to social media formats

Each social platform requires specific aspect ratios: Instagram feed posts (1:1 or 4:5), Twitter cards (2:1 or 16:9), LinkedIn banners (4:1), Facebook cover photos (2.7:1). Given a source image at an arbitrary resolution, calculating the crop dimensions that produce the required ratio prevents the platform from auto-cropping unfavorably.

How to Use the Aspect Ratio Calculator

  1. Enter the width and height in pixels.
  2. The simplified ratio, decimal value, and closest common format appear instantly.
  3. Use the preset buttons to quickly load common resolutions (1920×1080, 4K, etc.).
  4. Click "Copy" next to any row to copy the value.

Common Aspect Ratios