Calculate aspect ratios, resize dimensions proportionally, and convert between common display and video formats like 16:9, 4:3, 21:9, and more.
The Aspect Ratio Calculator helps you resize images, videos, and screens while preserving the correct proportions. Enter any two values — width, height, or the ratio itself — and instantly get the missing dimension, the simplified ratio, and comparisons to standard formats.
Aspect ratio defines the proportional relationship between width and height. A 16:9 ratio means for every 16 units of width, there are 9 units of height. Getting this right matters for video production, responsive web design, print layouts, photography cropping, and display purchasing decisions.
Whether you're preparing a YouTube thumbnail at 16:9, cropping a photo for Instagram's 4:5 portrait mode, or calculating the pixel dimensions for a 21:9 ultrawide monitor, this calculator gives you instant, accurate results with visual previews of how different ratios compare. It is also handy when you need to match a source file to a required output format without guessing. That keeps cropping and resizing consistent across different platforms.
Use this calculator when you need one dimension to scale from another without distorting the image. It is useful for video exports, responsive image slots, social media crops, presentation slides, and checking whether a source file matches a required screen format. That keeps resize decisions consistent instead of approximating by eye.
Aspect Ratio = W : H (simplified by GCD). New Height = New Width × (Original Height / Original Width). GCD computed via Euclidean algorithm.
Result: 16:9
GCD(1920, 1080) = 120. 1920/120 = 16, 1080/120 = 9, giving a 16:9 aspect ratio. To resize to 1280 wide: 1280 × (9/16) = 720, so 1280×720.
Aspect ratio is one of the most fundamental properties of any visual medium. From the earliest days of cinema (the Academy ratio of 1.375:1) to modern 8K displays (16:9), every screen, image, and video frame has a defined proportional relationship between width and height.
In web development, aspect ratios determine how images and videos respond to different viewport sizes. The CSS aspect-ratio property lets developers enforce consistent proportions. In video production, choosing the wrong export ratio means letterboxing or pillarboxing on the target display.
For social media: 1:1 (Instagram feed), 4:5 (Instagram portrait — maximizes screen space), 9:16 (Stories, Reels, TikTok), 16:9 (YouTube, Twitter video). For cinema: 1.85:1 (flat widescreen), 2.39:1 (anamorphic scope). For monitors: 16:9 (standard), 16:10 (productivity), 21:9 (ultrawide), 32:9 (super ultrawide). For print: 3:2 (standard photos), 5:4 (8×10 prints), 4:3 (old TV format).
Resolution (pixel count) and aspect ratio are independent concepts often confused. 1920×1080 and 1280×720 are different resolutions but share the same 16:9 ratio. When resizing, maintain the ratio to avoid distortion — change one dimension and calculate the other proportionally.
16:9 is the standard for HD, Full HD, and 4K video (1280×720, 1920×1080, 3840×2160). It's also the default for YouTube, streaming services, and modern TVs.
Instagram supports 1:1 (square), 4:5 (portrait), and 1.91:1 (landscape). Stories and Reels use 9:16 (vertical full-screen).
21:9 (actually 64:27) is used by ultrawide monitors. Common resolutions include 2560×1080 and 3440×1440. It provides more horizontal workspace for productivity and immersive gaming.
Always maintain the aspect ratio when resizing. If you change the width, calculate the new height proportionally (or vice versa). This calculator does that math automatically.
Most DSLR cameras shoot at 3:2 (6000×4000, 4500×3000). Older digital cameras and phones often use 4:3. Modern phones increasingly shoot at 16:9 or 3:2.
16:10 is slightly taller and was common in early widescreen laptops. 16:9 is now dominant for consumer displays. 16:10 remains popular for productivity laptops (e.g., MacBook Pro at 3024×1964).