By Ahsan Khowaja · Updated 27 October 2026
How to use the aspect ratio calculator
- Choose what you want to do: find the ratio of a size, or resize to a new width or height.
- Type the original width and height. Pixels are the usual unit, but centimetres, inches or any other unit work the same way, because a ratio has no units.
- Read the result. For a ratio you get the simplified form (16:9), the decimal form (1.778:1) and the closest standard ratio. For a resize you get the missing side, rounded to whole pixels.
To use the aspect ratio calculator from an image you already have, look up its width and height in the file's properties (on Windows: right-click › Properties › Details; on a Mac: open it in Preview › Tools › Show Inspector) and type them in.
How to calculate aspect ratio from width and height
An aspect ratio is the width divided by the height, written as two whole numbers. To get it, divide both sides by their greatest common divisor (GCD), the largest number that divides both exactly:
- 1920 × 1080: the GCD is 120, so 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9. The ratio is 16:9.
- 1080 × 1350: the GCD is 270, giving 4:5, a popular portrait size for feed posts.
- 1024 × 768: the GCD is 256, giving 4:3.
The decimal ratio is simply width ÷ height: 1920 ÷ 1080 = 1.778, written 1.778:1. It is the easiest way to compare two shapes. A bigger number means a wider picture, and anything below 1 is portrait.
Some screens are sold under a rounded name. A 2560 × 1080 ultrawide monitor is exactly 64:27 (2.370:1) but is marketed as 21:9 (2.333:1); its real shape is actually closer to the 2.39:1 cinema ratio. The calculator shows the exact ratio and the closest standard one, so you can see when a size is only approximately 21:9 or 16:10.
How to resize without stretching
To keep the same shape at a new size, scale both sides by the same factor:
- New height = new width × original height ÷ original width
- New width = new height × original width ÷ original height
Example: a 1920 × 1080 video resized to 1280 px wide becomes 1280 × 1080 ÷ 1920 = 720 px tall (1280 × 720, still 16:9). A 4032 × 3024 phone photo (4:3) made 1000 px wide becomes 750 px tall.
If the result isn't a whole number, the calculator rounds it, because images can only have whole pixels. When a site needs an exact frame such as 1080 × 1080 and your photo is a different shape, resizing alone can't make it fit: you have to crop. Our image resizer crops to an exact size or fits the picture inside it, in your browser.
Common aspect ratios and their pixel sizes
| Ratio | Decimal | Common sizes (px) | Used for |
|---|---|---|---|
| 16:9 | 1.778:1 | 1280 × 720, 1920 × 1080, 2560 × 1440, 3840 × 2160 | HD and 4K video, YouTube, TVs, most monitors |
| 9:16 | 0.5625:1 | 1080 × 1920 | Vertical video: TikTok, Reels, Shorts, Stories |
| 4:3 | 1.333:1 | 1024 × 768, 1600 × 1200, 4032 × 3024 | Most phone photos, iPads, older screens |
| 3:2 | 1.5:1 | 3000 × 2000, 6000 × 4000 | DSLR and mirrorless photos, 6 × 4 in prints |
| 1:1 | 1:1 | 1080 × 1080 | Square posts, profile pictures |
| 4:5 | 0.8:1 | 1080 × 1350 | Portrait feed posts |
| 3:4 | 0.75:1 | 1080 × 1440 | The tallest Instagram feed post |
| 16:10 | 1.6:1 | 1920 × 1200, 2560 × 1600 | Laptop and office monitors |
| 21:9 (≈64:27) | 2.37:1 | 2560 × 1080, 3440 × 1440 | Ultrawide monitors, cinema-style video |
Platform rules change, so check the current sizes before you post. Our guides to social media image sizes and Instagram image sizes link to each platform's own help pages.
16:9 aspect ratio calculator: sizes at a glance
For a 16:9 picture, the height is always the width × 9 ÷ 16 (or width ÷ 1.778). The standard 16:9 resolutions are 640 × 360, 854 × 480, 1280 × 720 (720p), 1920 × 1080 (1080p), 2560 × 1440 (1440p) and 3840 × 2160 (4K UHD). If your video editor or screen recorder shows any other 16:9 width, put it in the "new width" box to get the matching height.
The same boxes work as a 4:3 calculator: for a 4:3 picture, the height is the width × 3 ÷ 4, so 800 × 600, 1024 × 768, 1600 × 1200 and 2048 × 1536 are all 4:3.
Aspect ratio in centimetres, inches and print sizes
A ratio doesn't depend on units, so the aspect ratio calculator works in cm or inches as well as pixels. That makes the calculator handy for prints and frames:
- An 11 × 14 inch print is 11:14 (0.786:1), close to 4:5. A 4:3 phone photo has to be cropped to fill it.
- 6 × 4 inch (15 × 10 cm) prints are 3:2, the same shape as most camera photos, so those print without cropping.
- A4 paper (21 × 29.7 cm) is about 1:1.414, the same shape as every A size.
To work out how many pixels you need for a sharp print, use the print size calculator or the DPI calculator.
TV and monitor aspect ratios
TV and monitor sizes are measured diagonally, so two 27-inch screens with different aspect ratios have different widths and heights. A 55-inch 16:9 TV is about 47.9 × 27.0 inches. The screen size calculator turns a diagonal and a ratio into the width and height, and the PPI calculator shows how sharp the screen is.
Aspect ratio in CSS
On a website, the CSS aspect-ratio property keeps a box in proportion while its width changes, for example aspect-ratio: 16 / 9; for a video embed. It is supported by all current browsers (MDN: aspect-ratio). Giving images their width and height attributes does the same job for pictures: the browser reserves the right shape before the image loads, so the page doesn't jump.
