What an aspect ratio is
The aspect ratio of an image, a video or a screen is its width compared with its height, written as two numbers with a colon. 16:9 means 16 units wide for every 9 units high. The ratio describes the shape, not the size: 1280 × 720, 1920 × 1080 and 3840 × 2160 pixels are all 16:9, because each one is the same rectangle at a different resolution. A ratio above 1, like 16:9, is a landscape shape, 1:1 is a square, and a ratio below 1, like 9:16, is portrait.
You can also write a ratio as a single decimal by dividing the width by the height. 16 ÷ 9 is about 1.78, so 16:9 is also called 1.78:1. Decimals make it easy to compare shapes: the larger the number, the wider the picture.
How to find the aspect ratio of a size
Divide the width and the height by their greatest common divisor (GCD), the largest whole number that divides both without a remainder. What is left is the ratio in its simplest form.
Some sizes do not simplify to a familiar ratio. 1366 × 768 divides only by 2, so its simplest form is 683:384. As a decimal that is about 1.779, within 0.05% of 16:9, which is why the calculator also shows the nearest common ratio and how far off the size is. Sizes with decimals work too: a letter-size page of 8.5 × 11 inches is 17:22.
How to calculate a missing width or height
When you know the ratio a:b and one side, the other side follows from a simple proportion:
A 16:9 video that is 1280 pixels wide is 1280 × 9 ÷ 16 = 720 pixels high. A 4:5 image that is 1080 pixels wide is 1080 × 5 ÷ 4 = 1350 pixels high. Sometimes the answer is not a whole number: 1000 pixels wide at 16:9 gives 562.5 pixels. Pixels cannot be split, so the calculator rounds to 563 and shows the exact value next to it, which tells you that the rounded size is very slightly off the ratio. If you need an exact match, pick a width from the table of common sizes or a width that divides evenly by the first number of the ratio.
Common aspect ratios
These ratios cover most screens, videos and photos. The example sizes are calculated from the ratio, so each one matches it exactly.
| Ratio | Decimal | Shape | Example size in pixels |
|---|---|---|---|
| 1:1 | 1.00 | Square | 1080 × 1080 |
| 4:5 | 0.80 | Portrait | 1080 × 1350 |
| 2:3 | 0.67 | Portrait | 1080 × 1620 |
| 9:16 | 0.56 | Tall portrait | 1080 × 1920 |
| 4:3 | 1.33 | Landscape | 1024 × 768 |
| 3:2 | 1.50 | Landscape | 1620 × 1080 |
| 16:10 | 1.60 | Landscape | 1920 × 1200 |
| 16:9 | 1.78 | Widescreen | 1920 × 1080 |
| 21:9 | 2.33 | Ultrawide | 2520 × 1080 |
Social networks each ask for their own image and video sizes. Our social media image sizes page lists the current sizes with a link to each platform's own documentation.
Standard video resolutions and their ratios
Television and video formats are fixed by standards bodies. High definition and ultra high definition television are all 16:9, while the digital cinema formats are a little wider.
| Name | Pixels | Aspect ratio | Defined in |
|---|---|---|---|
| 720p | 1280 × 720 | 16:9 | SMPTE ST 296 |
| 1080p | 1920 × 1080 | 16:9 | ITU-R BT.709 |
| 4K UHD | 3840 × 2160 | 16:9 | ITU-R BT.2020 |
| 8K UHD | 7680 × 4320 | 16:9 | ITU-R BT.2020 |
| DCI 2K (cinema) | 2048 × 1080 | 256:135, about 1.9:1 | Digital Cinema Initiatives |
| DCI 4K (cinema) | 4096 × 2160 | 256:135, about 1.9:1 | Digital Cinema Initiatives |
So "4K" on a TV and "4K" in a movie theater are not quite the same shape. The p in 720p and 1080p stands for progressive scan, and the number is the height in pixels, so 1440p means a picture 1440 pixels high, such as 2560 × 1440.
Why 21:9 is not always exactly 21:9
21:9 simplifies to 7:3, or 2.33:1. Screens sold as 21:9 do not always match it exactly. LG, for example, has sold a 34 inch 3440 × 1440 monitor as 21:9; that size simplifies to 43:18, or about 2.39:1. 2560 × 1080 simplifies to 64:27, about 2.37:1. Treat 21:9 as the name of a shape, and use the exact pixel size when you make content for a specific screen.
Tips for resizing without distortion
- Lock the ratio before you resize. Change one side and let the other follow, and the picture keeps its shape. With the lock on in the calculator, typing a new width updates the height right away.
- Changing the ratio means cropping or adding space. A 4:3 photo cannot become 16:9 without either cutting off part of the top and bottom or adding bars or a background at the sides. Stretching it distorts faces and circles.
- Make images smaller, not larger. Scaling down keeps detail, scaling up cannot add any. Start from the largest version you have. Our image resizer resizes photos in your browser, with the ratio kept.
- Watch out for rounding. When a calculated side is not a whole number, the rounded size is a fraction of a pixel off. You will not see the difference, but when a platform or a client asks for an exact size, use that size or pick an exact one from the table.
- Portrait is just the ratio turned around. 9:16 is 16:9 on its side. Swap sides flips width and height in one click.
How to use the aspect ratio calculator
- 1To find a ratio, type the width and the height. The simplest ratio, its decimal and the nearest common ratio appear at once.
- 2To find a missing side, pick a ratio from the chips or type your own, then type the width or the height. The ratio locks, and the other side is calculated.
- 3Check the shape in the preview and pick a size from the table of common sizes, or use Swap sides for portrait.
- 4Copy the result, or copy a link that opens the calculator with your numbers.
Frequently asked questions
How do I calculate an aspect ratio?
Find the greatest common divisor (GCD) of the width and the height, the largest whole number that divides both, and divide both sides by it. For 1920 × 1080 the GCD is 120, and 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, so the aspect ratio is 16:9. The calculator does this for you as soon as you type both sides.
How do I find the height for a 16:9 width?
Multiply the width by 9 and divide by 16. A 16:9 image that is 1280 pixels wide is 1280 × 9 ÷ 16 = 720 pixels high. To go the other way, multiply the height by 16 and divide by 9. With the ratio locked, the calculator fills in the other side while you type.
Is 4K 16:9?
4K UHD for TVs and video is 3840 × 2160 pixels, which is exactly 16:9; ITU-R Recommendation BT.2020 defines it that way. Digital cinema 4K is 4096 × 2160 pixels, which is 256:135, about 1.9:1, so it is a little wider than 16:9.
What is the difference between 16:9 and 16:10?
16:10 is a slightly taller shape. It simplifies to 8:5, or 1.6:1, while 16:9 is about 1.78:1. At the same width of 1920 pixels, 16:10 is 1200 pixels high and 16:9 is 1080 pixels high, so a 16:10 screen has 120 more rows of pixels.
Why does the calculator say 683:384 instead of 16:9?
Because the size is not exactly 16:9. 1366 × 768 divides only by 2, so its simplest form is 683:384, or about 1.779:1. That is within 0.05% of 16:9, so the calculator lists 16:9 as the nearest common ratio.
What is the 9:16 aspect ratio?
9:16 is 16:9 turned on its side: a tall, vertical shape. 1080 × 1920 pixels is 9:16, the same as a 1920 × 1080 video rotated by 90 degrees. Use Swap in the calculator to turn any size from landscape to portrait. For the exact sizes each social network asks for, see our social media image sizes page.
Does changing the aspect ratio stretch my image?
Only if you force it. To go from one ratio to another without distortion you either crop part of the image or add bars or a background around it. Resizing to a new size with the same ratio keeps the picture exactly as it is, just larger or smaller.