About the Aspect Ratio Calculator
An aspect ratio is the width of a picture or screen compared with its height. This calculator does three things with it. It reduces any width and height to a ratio like 16:9 and tells you the closest common ratio. It scales a size up or down, so you type a new width and the new height follows. And it works out the largest crop of a chosen ratio that fits inside your picture, with the position to start from. Pixel answers are rounded to whole pixels, so converting back can be one pixel out. The closest-common-ratio line is a nearest match from a short list, and the page shows how far off it is. It only does the arithmetic and does not open or resize images.
Updated September 2026
How to use the Aspect Ratio Calculator
- 1Type the width and height in pixels, or tap a common size.
- 2Read the ratio, its decimal value and the closest common ratio.
- 3To resize, type a new width or a new height and read the other side.
- 4To crop, tap a target ratio such as 1:1 or 16:9, or type your own like 1.91:1.
- 5Copy the summary if you want to paste it into a note or a brief.
How aspect ratio is calculated
Take the width and the height, find the largest whole number that divides both, and divide each side by it. A 1080 × 1920 phone screen shares a divisor of 120, so its ratio is 9:16. Some sizes do not reduce to anything tidy: 1366 × 768 becomes 683:384, which is why the page also gives the decimal (1.7786) and the nearest common ratio (16:9).
The decimal form is the width divided by the height. Anything above 1 is landscape, exactly 1 is square, and anything below 1 is portrait.
Common ratios and where they're used
The one-tap sizes on this page include HD, 4K, story, portrait post, link preview and banner dimensions.
- 1:1 square: profile pictures and feed posts
- 4:3 and 3:2: older screens, photo prints and many cameras
- 16:9: monitors, televisions and video sites
- 16:10: some laptop displays
- 21:9: ultrawide monitors and cinema-style video
- 4:5 and 9:16: tall posts, stories and short video
Resizing without stretching
Stretching happens when width and height are scaled by different amounts. Keep the ratio locked: multiply both sides by the same factor. In the Resize section you type either side and the other is calculated, rounded to the nearest whole pixel. Because of rounding, a size like 1080 wide from a 1080 × 1920 original gives 608 rather than 607.5 tall.
To apply the new size to a real picture, use the Image Resizer with the numbers you found here.
Cropping to a ratio
Cropping removes part of the picture so it fits a different shape. Choose your target ratio and the calculator finds the biggest rectangle of that shape that fits inside the original, centred. From a 1920 × 1080 picture, a square crop is 1080 × 1080 starting at x = 420. Read the start position as pixels from the left and top edges.
Then open Crop Image to make the crop. If the picture will be printed for an ID or a form, the Passport Size Photo Maker handles the fixed sizes for you. Wherever a size is quoted in inches or centimetres instead of pixels, the Unit Converter helps you switch.
Features
- Reduces any size to a ratio such as 16:9
- Closest common ratio with the difference shown
- New width or height that keeps the ratio
- Largest centred crop and its start position
- One-tap sizes for HD, 4K, stories, posts and banners
- Live drawing of the rectangle in your ratio
- Runs in your browser
Frequently asked questions
What is an aspect ratio?
It is the proportion between width and height, written as two numbers such as 16:9. A 1920 × 1080 screen and a 1280 × 720 screen look the same shape because both reduce to 16:9. Only the number of pixels differs.
How do I calculate the aspect ratio of an image?
Divide the width and the height by their greatest common divisor. For 1920 × 1080 that divisor is 120, giving 16:9. Enter your numbers at the top of this page to see the reduced form and the decimal value 1.7778.
What aspect ratio is 1920×1080?
It is 16:9, the widescreen shape used by most monitors, TVs and online video. 1366 × 768 is very close to it, off by about 0.05 %, but it does not reduce exactly to 16:9.
How do I resize without stretching?
Change width and height by the same factor. Type the width you want in the Resize box and the height is filled in for you, rounded to whole pixels. Going from 1920 × 1080 to a width of 1280 gives a height of 720.
What ratio should Instagram posts and stories use?
Feed posts are commonly 1:1, 4:5 (1080 × 1350) or landscape at about 1.91:1, and stories and reels use 9:16 (1080 × 1920). Platforms change their rules, so check the current guidance before you export.
What is the difference between 16:9 and 16:10?
16:10 is a little taller: at the same width, a 16:10 screen has about 11 % more height. 1920 × 1200 is 16:10, while 1920 × 1080 is 16:9. Many laptops use 16:10 for extra vertical space.
How does the crop calculation work?
It keeps the full width or full height, whichever runs out first, and trims the other side so the shape matches your target. The crop is centred, and the start position is rounded down to a whole pixel.
Why is the ratio shown with decimals sometimes?
Ratios can only be reduced to whole numbers when the width and height are whole numbers. If you type decimals, the page shows the decimal ratio instead.