A fast, local aspect ratio calculator
Whether you are cropping photos, designing responsive web layouts, or setting up a video project, getting your dimensions right is critical. This aspect ratio calculator helps you instantly find the exact proportions of any image or screen, and scale dimensions up or down without distorting the final result.
Because this tool runs entirely in your web browser, all math is computed locally on your device. You get instant results as you type, and no data is ever sent to a server.
Calculate aspect ratio from resolution
If you have an image's exact pixel dimensions but don't know its shape, the top section of the tool will find it for you. Simply enter the width and height, and the calculator will determine the greatest common divisor to reduce the numbers to their simplest integer form.
For example, entering a width of 2560 and a height of 1440 instantly reveals a ratio of 16:9.
Alongside the standard integer ratio, the tool provides:
- Decimal ratio: This format (like
1.78:1) is standard in the film industry and is useful when writing CSS (e.g.,aspect-ratio: 1.78). - Orientation: A quick check to confirm if your dimensions result in a landscape, portrait, or square layout.
Resize keeping aspect ratio
Scaling an image incorrectly leads to stretched or squished graphics. The resize section of the tool prevents this by doing the proportional math for you.
To resize keeping aspect ratio, enter your target proportion (such as 16:9 or 4:5) in the ratio field. Then, type your desired new width. The calculator will instantly output the exact height required to maintain that shape. You can also work in reverse: type a new height, and the tool will calculate the correct width. This is especially useful when you need to fit an image into a specific layout container but want to ensure the proportions remain mathematically perfect.
Common proportions and presets
Different platforms and mediums rely on specific standard ratios. The tool includes one-click presets for the most common digital formats, functioning instantly as a 16:9 calculator or a quick reference for social media sizes.
- 16:9 (Widescreen): The global standard for HD, 4K video, YouTube, and most modern computer monitors.
- 9:16 (Vertical Video): The exact inverse of widescreen, used heavily for TikTok, Instagram Reels, and YouTube Shorts.
- 4:3 (Standard): The traditional television and monitor format, still widely used in digital photography (especially Micro Four Thirds cameras) and older presentations.
- 1:1 (Square): Perfect symmetry, popularized by Instagram feeds and commonly used for profile pictures and grid layouts.
- 3:2 (Photography): The standard ratio for 35mm film and most modern DSLR and mirrorless camera sensors.
- 21:9 (Ultrawide): A cinematic format used for ultrawide gaming monitors and anamorphic film presentations.
Understanding pixel aspect ratio
When working with digital dimensions, it helps to understand the concept of pixel aspect ratio (PAR). This describes the physical shape of the pixels themselves.
In the early days of digital video (like DV and DVD), pixels were often rectangular, meaning an image that looked square on a computer monitor might look stretched on a television. Today, almost all modern web design, digital photography, and high-definition video use a 1:1 pixel aspect ratio—meaning the pixels are perfectly square. This calculator assumes square pixels, which is the correct standard for modern software and web development.
If you need to apply these calculations to actual files, you can use the Change Aspect Ratio tool to crop or pad an image to a new shape. If you just need to scale an image file's resolution based on the numbers you calculated here, try the Resize Image tool. You can also verify your own monitor's dimensions using the Screen Resolution test.