Aspect Ratio Calculator
Enter a width and height to get the aspect ratio, such as 16:9. It works for pixels as well as real sizes in mm, cm or m. You can also find the missing width or height from a ratio.
What an aspect ratio is
The aspect ratio of an image or a screen is the ratio of its width to its height, written as two numbers separated by a colon, such as 16:9. A 16:9 picture is 9 units tall for every 16 units of width.
Pixels, and also real sizes of screens and LED walls
You can choose px (pixels), mm, cm or m as the unit of length. So you can work out the ratio from the size of an image or a video in pixels, and also from the real dimensions of a projector screen, a monitor or an LED wall.
- Enter the width and the height in the same unit (both in cm, both in m, and so on). The unit does not affect the ratio: 1920 mm × 1080 mm, 192 cm × 108 cm and 1.92 m × 1.08 m are all 16:9.
- Changing the unit does not change the numbers you typed. Only the displayed unit changes.
- Pixels must be whole numbers. In mm, cm and m you can enter decimals (up to 9 digits before the decimal point and 6 decimal places), and they are calculated exactly.
- Example: an LED wall 4.8 m wide and 2.7 m tall is 16:9. A screen 160 cm wide and 120 cm tall is 4:3.
- From a ratio and one length you can also find the other length. For a 16:9 LED wall that is 4.8 m wide, the height is 2.7 m.
How it is calculated
- Finding the ratio: divide the width and the height by their greatest common divisor (the largest number that divides both). The greatest common divisor of 1920 and 1080 is 120, so 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, which gives 16:9.
- Finding the height: height = width × ratio height ÷ ratio width. For 16:9 and a width of 1280, 1280 × 9 ÷ 16 = 720.
- Finding the width: width = height × ratio width ÷ ratio height. For 16:9 and a height of 1080, 1080 × 16 ÷ 9 = 1920.
Common aspect ratios
| Ratio | Width ÷ height | Where you see it |
|---|---|---|
| 1:1 | 1.00 | Square images |
| 5:4 | 1.25 | Some monitors, some photo prints |
| 4:3 | 1.33 | Older TVs and monitors, tablets |
| 3:2 | 1.50 | Still photography |
| 16:10 | 1.60 | Computer monitors |
| 16:9 | 1.78 | Television, video, computer monitors |
| 2:1 | 2.00 | Some phone screens |
| 21:9 | 2.33 | Ultrawide monitors |
A tall screen swaps the numbers, for example 9:16.
When "about 16:9" is shown
Some screen resolutions do not reduce to a neat ratio. For example, 1366 × 768 reduces to 683:384, which is hard to read. But width ÷ height is about 1.7786, close to the 1.7778 of 16:9, so it is called about 16:9.
The calculator shows a close common ratio from the table above, such as "About 16:9 (0.05% off)", only when it is within 1%. This is an approximation: the exact ratio is the simplified one (683:384). If the ratio is more than 1% away from every common ratio, nothing is shown.
Ultrawide screens such as 2560 × 1080 are often called 21:9, but exactly they are 64:27, which is about 1.6% away from 21:9, so this calculator does not show 21:9 as a close ratio for them.
Real dimensions and decimals
Real measurements do not always give a neat ratio (for example, 1.2345 m × 0.9877 m). When a length with decimals reduces to a ratio of large whole numbers (more than 1,000), the calculator does not show an awkward ratio such as 12345:9877. It shows width ÷ height as a decimal instead (for example, 1.2499:1). A close common ratio (such as about 5:4) is still shown next to it when it is within 1%.
Things to know
- In pixels, the width and the height must be whole numbers of 1 or more (up to 999,999,999). In mm, cm and m, any number greater than 0 works.
- When you find a length from a ratio, both the ratio and the length can have decimals (a ratio such as 2.39:1 works). The result is shown to 2 decimal places. In pixels, the result rounded to a whole number is shown too, because a pixel count is a whole number.
- A ratio cannot contain 0 or a negative number.
- To work with the sensor size of a camera, see the Camera Field of View Calculator or the 35mm Equivalent Focal Length Calculator.
Source
The definition (a ratio of width to height, written width:height) and the examples of common ratios follow Wikipedia, "Aspect ratio (image)": https://en.wikipedia.org/wiki/Aspect_ratio_(image) (read on November 1, 2026; only the first part of that long page could be read word for word). It is an explanatory article, not a standard.
Frequently asked questions
What is the aspect ratio of 1920×1080?
16:9. 3840×2160 (4K) also reduces to 16:9.
What is the height of a 16:9 image that is 1280 wide?
- Use "A length from a ratio", enter 16 and 9, choose "Width" as the known length and enter 1280.
How do I resize an image without changing its aspect ratio?
Find the ratio from the original width and height, then enter the new width (or height) to get the other length. When it does not divide evenly, use a rounded whole number; the ratio will change very slightly.
What is the difference between 4:3 and 16:9?
Width ÷ height is about 1.33 for 4:3 and about 1.78 for 16:9, so 16:9 is the wider screen.