ToolPetal
Aspect ratio calculator
- Runs on your device
- Nothing uploaded
- Free, no sign-up
Find the aspect ratio
The image is read on your device and not uploaded.
Resize and keep the ratio
| Width | Height | Pixels |
|---|
How to use the aspect ratio calculator
- Find a ratio. Type a width and height, such as 1920 and 1080, or open an image to read its size. The ratio appears in its simplest form (16:9), as a decimal (1.7778:1), and with the closest common ratio if it is not exact.
- Pick a ratio to resize at. Press a preset such as 16:9 or 9:16, type your own, or press Resize at this ratio to use the one you just found.
- Type a new width or height. The other side fills in so the shape stays the same. Whichever box you typed in last is kept and the other one changes.
- Check the sizes table. It lists common sizes at your ratio and says whether each one comes out in whole pixels.
Worked examples
| Size or task | Working | Answer |
|---|---|---|
| 1920 x 1080 | both divide by 120 | 16:9 |
| 1080 x 1350 | both divide by 270 | 4:5 |
| 1366 x 768 | simplest form 683:384, 1.7786:1 | close to 16:9 |
| 16:9 at 1280 wide | 1280 x 9 / 16 | 720 high |
| 9:16 at 1920 high | 1920 x 9 / 16 | 1080 wide |
The formula
An aspect ratio is width divided by height, written as two whole numbers. To simplify it, divide both by their greatest common divisor: 1920 and 1080 share 120, which gives 16:9. To resize, new height = new width x ratio height / ratio width, and new width = new height x ratio width / ratio height. When the answer is not a whole number of pixels the tool rounds it and tells you the exact value, so you can pick a size that divides evenly instead.
Common aspect ratios
| Ratio | Decimal | Used for |
|---|---|---|
| 16:9 | 1.78 | HD and 4K video, YouTube, most monitors and TVs |
| 9:16 | 0.56 | Vertical video: Reels, TikTok, Shorts, Stories |
| 4:3 | 1.33 | Older TVs, many tablets, slides |
| 1:1 | 1 | Square posts and profile pictures |
| 4:5 | 0.8 | Tall feed posts |
| 3:2 | 1.5 | Most camera photos, 6 x 4 prints |
| 21:9 | 2.33 | Ultrawide monitors and a cinema look |
Questions
How do I calculate an aspect ratio?
Divide the width and the height by their greatest common divisor. For 1920 x 1080 that is 120, so the ratio is 16:9. Type the two sizes into the calculator and it does this for you.
What is the height of a 16:9 image that is 1280 wide?
Multiply the width by 9 and divide by 16: 1280 x 9 / 16 = 720. So 1280 x 720 is 16:9.
What aspect ratio is 1080 x 1920?
1080 x 1920 is 9:16, the vertical video size used for Reels, TikTok, Shorts and Stories.
Why does my size show an odd ratio like 683:384?
Some screen sizes are not an exact common ratio. 1366 x 768 simplifies to 683:384, which is 1.7786:1, so the tool shows it as close to 16:9.
Can I find the ratio of an image I have?
Yes. Open the image with the file picker and its width and height fill in. The image is read on your device and is not uploaded.
What does Round to whole pixels do?
Images and video need whole pixels, so the new width or height is rounded. If rounding changes the ratio slightly, the tool shows the exact value. Turn it off to see decimals.