Pick a ratio, type one side, read the other. That is the whole aspect ratio calculator. Seven presets cover 16:9, 9:16, 4:3, 1:1, 4:5, 21:9 and 3:2, and the two ratio fields take any other numbers, decimals included. You get the missing side of an image or a video without opening a design tool.
Why 1000 px at 16:9 gives 563
The tool rounds to whole pixels. 1000 px at 16:9 is exactly 562.5, and the height field shows 563. A monitor sold as 3440 x 1440 is not exact 21:9 either: at 3440 px wide, the 21:9 height is 1474.
The calculation runs one way. You give a ratio and one side, and the tool returns the other side. It cannot read a ratio from two sizes, so typing 1920 and 1000 will not tell you the ratio of that pair. Zero and negative values are not checked. If you clear a ratio field, the math uses 16 or 9 until you type a new number.
Sizes worth keeping at hand
- Instagram portrait post, 4:5: 1080 px wide gives 1350 px tall.
- Reel or TikTok clip at 9:16 and 1080 px wide needs 1920 px of height.
- DSLR photo in 3:2. 6000 px across, 4000 px down.
- For an ultrawide mockup, 21:9 at 2560 px gives 1097 px.
- Cinema: type 2.39 and 1, enter 1920 as the width, and the height is 803.
Four clicks through the aspect ratio calculator
- Click a preset (16:9, 9:16, 4:3, 1:1, 4:5, 21:9 or 3:2), or type your own numbers into the two Ratio (W:H) fields.
- Enter the Width in pixels. The Height fills in at once.
- To work backwards, type a Height instead. The width updates.
- Check the box under Visual proportion. It draws the shape with the size inside, and the badge above it shows the ratio as a decimal, for example 16 : 9 (1.78 : 1).
A click on a preset keeps the current width and changes the height. The preview box always scales to a longest side of 180 px, whatever the real size is.
No image goes in, no request goes out
Each calculation is a multiplication and a division in your browser. When you type or click a preset, no request is sent. You can confirm that in the network panel of your developer tools. The tool reads no image, writes no file, does not use the clipboard and does not store your numbers. It does not resize pictures either. It only works with numbers.