What is aspect ratio?
Aspect ratio describes the proportional relationship between an image's width and height, expressed as two numbers separated by a colon — for example 16:9 or 4:3. It tells you the shape of the image, not its actual dimensions. A 1920×1080 video and a 640×360 video both have a 16:9 ratio — they're the same shape, just different sizes. Aspect ratio is fundamental to photography, video production, web design, and print layout.
Finding a missing dimension
Select "Find missing dimension", enter either the width or the height (leave the other blank), then type a ratio in the W:H field or click a preset. The calculator will compute the missing dimension that maintains the given ratio. This is useful when you need to resize an image to a specific width and want to know the correct height to avoid distortion, or when preparing images for a platform with a required aspect ratio.
Common aspect ratios
16:9 (1.778) — HD and 4K video, YouTube, most monitors and TVs. 4:3 (1.333) — Traditional TV, standard definition video, iPad displays. 1:1 (1.0) — Square format, Instagram posts, avatar images. 21:9 (2.333) — Ultrawide monitors, cinematic films. 3:2 (1.5) — 35mm photography, most DSLR and mirrorless cameras. 9:16 (0.5625) — Portrait video, Instagram and TikTok Stories.
Simplifying a ratio
Select "Find ratio" and enter both width and height. The calculator divides both values by their greatest common divisor (GCD) to produce the simplest whole-number ratio — for example, 2560×1440 simplifies to 16:9. It also shows the decimal ratio (width ÷ height) which is convenient for CSS aspect-ratio property comparisons. If the numbers don't simplify to a small ratio (e.g. 1200×628 from an Open Graph image), the decimal representation is most useful.