Guide
How to use the aspect ratio calculator
The calculator has two pairs of boxes. The original size is the width and height you already have, for example a 1920x1080 video frame or a 4000x3000 photo. As soon as both values are in, the tool shows the simplified ratio (16:9 or 4:3), its decimal form (1.778 or 1.333), the orientation, and the common name of that ratio when one exists.
The new size pair is for resizing. Type only the width you need and the height fills in automatically, or type only the height and the width follows. Because the second pair is always derived from the first, the result keeps exactly the same proportions, so nothing looks squashed or stretched. The preset chips load the most common ratios in one click, and Swap flips landscape to portrait.
How aspect ratio is calculated
An aspect ratio is simply width divided by height, expressed as two whole numbers. To simplify it, divide both values by their greatest common divisor. For 1920x1080 that divisor is 120, giving 16:9. For 1280x720 it is 80, also giving 16:9, which is why both resolutions fit the same screen shape.
To resize while keeping a ratio, use one of these two formulas:
new height = new width x original height / original widthnew width = new height x original width / original height
Example: a 4000x3000 photo needs to be 1200 pixels wide. 1200 x 3000 / 4000 = 900, so the new size is 1200x900. Some results are not whole numbers; the tool rounds to the nearest pixel and tells you the exact value so you can decide whether a one-pixel difference matters for your export.
Odd resolutions such as 1366x768 simplify to unfriendly numbers (683:384). In those cases the calculator shows the nearest standard ratio, here 16:9, and lists the exact ratio underneath, because in practice you almost always want the standard name.
Where aspect ratios matter
Video
YouTube, TVs, and most monitors use 16:9. Vertical formats for YouTube Shorts, Instagram Reels, and TikTok use 9:16, which is the same frame turned on its side (1080x1920). Cinema uses wider ratios such as 1.85:1 and 2.39:1, which is why films show black bars on a 16:9 television. If you export in the wrong ratio the platform will letterbox or crop your video, so check the target ratio before you render.
Photos and print
Most DSLR and mirrorless cameras shoot 3:2, while phones and many compact cameras shoot 4:3. Print sizes rarely match either: a 4x6 print is 3:2, but 5x7 and 8x10 are not, so part of the image is cropped. Calculating the print ratio in advance tells you how much you will lose at the edges.
Social media and web
Instagram feed posts accept 1:1, 4:5, and 1.91:1; Stories use 9:16; link preview images on Facebook, LinkedIn, and X work best at 1.91:1 (1200x630). Web layouts often reserve fixed slots for hero images and thumbnails, and an image that does not match the slot ratio gets cropped by CSS. Resizing with the ratio locked avoids blurry, distorted, or unexpectedly cropped images.
Screens and design
Laptops moved from 16:9 to 16:10 and 3:2 in recent years, and ultrawide monitors are 21:9 or 32:9. When you design wallpapers, presentations, or UI mockups, start from the target ratio so nothing is cut off. The common aspect ratios table lists resolutions for each of these.
Why use this tool
- Fill any three values and the fourth is computed instantly, with exact and rounded results.
- Names the ratio and points to the closest standard when a resolution is unusual.
- Dark mode, mobile friendly, keyboard friendly. Press T to switch themes.
- No uploads, no accounts, no limits. The image aspect ratio finder reads your file locally in the browser and never sends it anywhere.
- Free forever. Static pages that load in well under a second, even on a slow connection.
Questions or a missing feature? Write to hello@aspectratiocalculator.com.