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Free Calculator

Aspect Ratio Calculator

Two modes: enter width × height to find the simplified ratio, or enter a ratio and one dimension to calculate the missing side. Includes 12 common ratio presets and a visual shape preview.

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What Are Aspect Ratios Used For?

Aspect ratios appear everywhere in visual media. Every screen, video, photograph, and printed page has a shape — and that shape determines how content fits, how it crops, and how it looks on different displays. Understanding aspect ratios helps you avoid black bars, unexpected cropping, and distorted images.

Designers use aspect ratios to maintain consistent proportions when resizing. Video editors set project dimensions based on delivery format (16:9 for YouTube, 9:16 for TikTok). Photographers choose crop ratios before printing. Print designers calculate scaled dimensions for images and layouts. This calculator handles all of these cases.

Common Aspect Ratios and Their Uses

How the Ratio Simplification Works

When you enter width and height, the calculator finds the greatest common divisor (GCD) of the two numbers and divides both by it to get the smallest integer ratio. For example, 1920 and 1080 share a GCD of 120, so 1920/120 = 16 and 1080/120 = 9 — giving you 16:9. For non-integer ratios (like the 1:1.414 of A4 paper), the decimal ratio is shown alongside the simplified integer form.

For pixel-level measurements on screen, use the pixel ruler to measure actual dimensions, then paste them here to find the ratio. The unit converter helps if you need to switch between pixels, mm, and inches.

Frequently Asked Questions

An aspect ratio is the proportional relationship between width and height, expressed as W:H (e.g., 16:9). It describes the shape of a rectangle without specifying actual dimensions — a 1920×1080 screen and a 1280×720 screen both have a 16:9 aspect ratio.
16:9 is the dominant video aspect ratio — used by YouTube, Netflix, HDTV, and most smartphone cameras. 21:9 (ultrawide) is used for cinematic content. Older formats include 4:3 (standard TV) and 1.85:1 (theatrical film).
If you know the ratio (e.g., 16:9) and the width (e.g., 1920 px), divide the width by the first ratio number and multiply by the second: 1920 ÷ 16 × 9 = 1080. Use the "Ratio → Dimension" mode in this calculator to do it automatically.
A4 paper (210 × 297 mm) has an aspect ratio of approximately 1:1.414 — also written as 1:√2. All ISO A-series paper sizes share this ratio, so A4, A3, and A5 are all the same shape.
Common social media aspect ratios: Instagram square 1:1, Instagram portrait 4:5, Instagram landscape 1.91:1, Twitter/X cards 2:1, Facebook cover 2.7:1, Pinterest 2:3, TikTok and Reels 9:16.
Divide width by height to get a decimal ratio, then find the nearest simple fraction. For example, 1920÷1080 = 1.7778 ≈ 16/9. Or enter the dimensions in the "Dimensions → Ratio" mode above and the calculator simplifies it automatically using GCD.