Aspect ratio calculator
Find a ratio from width and height, or scale to a new size.
Runs in this tab. The file stays here.
- Ratio
- 16:9
- Decimal
- 1.7778
- Scaled size
- 1280 × 720
This runs in your browser. Nothing is uploaded.
About Aspect ratio calculator
Reduce a width and height to its simplest ratio (1920 by 1080 gives 16:9), or take a ratio and one new dimension and get the other. The math runs in your browser.
There are two modes. Find ratio from size takes a width and height, divides both by their greatest common divisor, and shows the result, so 1920 by 1080 becomes 16:9 and 1000 by 800 becomes 5:4. Scale to new size lets you type a ratio yourself, or pick a preset (16:9, 4:3, 3:2, 1:1, 21:9, 9:16, or 4:5), for when you already know the shape you need. In both modes the output also shows the ratio as a decimal to four places (16:9 is 1.7778), which is the number video and CSS settings often want.
The New width and New height boxes are what turns a ratio into a size. Type a width and the height is calculated for you; type a height and you get the width. Filling in one clears the other, so you work from whichever side you know. The result appears as Scaled size, and a small preview box redraws in the same proportions. Values are rounded to the nearest whole pixel, which means a scaled dimension can be a fraction of a pixel off the true ratio, and a ratio like 16:9 at 1000 pixels wide gives a height of 563, not exactly 562.5.
Ratios reduce only when both numbers are whole. If you enter decimals, such as a sensor measured in millimetres, it can't reduce them, and it shows the figures as entered along with a note. The tool does the arithmetic and nothing else: it doesn't open images, so for resizing a file to the result use Resize, or Crop with a ratio preset when you need to cut a photo to shape instead of squashing it.
How to use Aspect ratio calculator
- 1Choose Find ratio from size and enter the width and height, or choose Scale to new size and set a ratio or preset.
- 2Type the new width or the new height you want.
- 3Read the ratio, the decimal, and the Scaled size.
What it won't do
- Whole-number ratios only reduce; decimal sizes are shown as entered.
- Scaled sizes are rounded to the nearest pixel.
- Calculates only; doesn't read or resize image files.
Common questions
Why is my scaled height not a whole number?
Most ratios don't divide evenly into your width. The page rounds to the nearest pixel, so 1000 wide at 16:9 gives 563 high, when the exact figure is 562.5. Pick a width that divides cleanly (a multiple of 16 for 16:9) if you need an exact fit.
Can I use it with decimals or units?
You can type decimals, but they can't be reduced to a whole-number ratio, so the page shows what you entered and the decimal value. There are no units; the numbers mean whatever you decide they mean, pixels, millimetres, or inches.
Does it resize my image?
No. It only calculates dimensions. Take the result to the resize or crop tool to change a real file.
What is the decimal figure for?
It's width divided by height. Some software, and CSS properties like aspect-ratio, accept it directly, and it makes two ratios easy to compare: 1.7778 for 16:9 and 1.6 for 16:10.
Related tools
Why this one doesn't upload your file
There is no server to upload to. This page is a static file, and the work happens in your browser using the same graphics and WebAssembly code that renders every other site you visit. Your file is read from disk into memory, processed, and handed back as a download. Once the page has loaded you can disconnect from the network entirely and it keeps working. The longer explanation