Aspect ratio calculator
Enter a width and height to see their aspect ratio, such as 16:9, and the nearest standard ratio. Then type a new width or height and the other side is calculated for you, so images, videos and screens keep their shape. Pick a preset, read the size from an image, or choose from the list of common resolutions.
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How to use it
- Enter the original width and height, pick a preset such as 16:9, or read the size from an image.
- Read the aspect ratio, its decimal value and the nearest standard ratio. The preview shows the shape.
- Type a new width or a new height under Resize. The other side is calculated so the picture is not stretched.
- Choose even numbers for video, or pick one of the common sizes from the list with Use.
Why use this tool
Ratio from any size
Simplifies the width and height to the smallest whole numbers, such as 1920 × 1080 to 16:9, and shows the decimal ratio.
Nearest standard ratio
Sizes like 1366 × 768 do not simplify neatly. The calculator tells you they are close to 16:9 and by how much.
Resize without stretching
Type a new width or height and get the other side at once, rounded to whole pixels, even numbers for video, or decimals.
Presets and common sizes
One click for 16:9, 4:3, 1:1, 9:16, 4:5, 21:9 and cinema ratios, plus well-known resolutions such as 1080p, 4K and story sizes.
Read size from an image
Choose a photo or screenshot and its width and height are filled in. The image stays on your device.
CSS ready
Copy the aspect-ratio rule for your stylesheet to keep videos and cards in shape on any screen.
What is an aspect ratio?
The aspect ratio is the proportion between the width and the height of a picture, video or screen. It is written as two numbers with a colon, width first. 16:9 means 16 units wide for every 9 units high, whatever the actual size: 1280 × 720 and 3840 × 2160 are both 16:9.
Keeping the ratio when you resize means the picture is not stretched or squashed. If the ratio of the new size differs, the picture has to be cropped or get bars on the sides.
Common aspect ratios and where they are used
| Ratio | Decimal | Used for |
|---|---|---|
| 16:9 | 1.78 | TV, YouTube, most monitors and laptops, presentations |
| 4:3 | 1.33 | Older TVs and monitors, iPad, many compact cameras |
| 3:2 | 1.5 | DSLR and mirrorless photos, 6 × 4 inch prints |
| 1:1 | 1 | Square social posts and profile pictures |
| 4:5 | 0.8 | Portrait posts in social feeds |
| 9:16 | 0.56 | Stories, Reels, TikTok and Shorts, phone screens held upright |
| 16:10 | 1.6 | Many laptops and office monitors |
| 21:9 | 2.33 to 2.39 | Ultrawide monitors and widescreen films |
How to calculate an aspect ratio by hand
- Find the greatest common divisor of the width and height. For 1920 and 1080 it is 120.
- Divide both numbers by it: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, so the ratio is 16:9.
- To resize, divide the new width by the ratio width and multiply by the ratio height: 1600 ÷ 16 × 9 = 900.
- For a decimal ratio, divide the width by the height: 1920 ÷ 1080 = 1.78.
Why use even numbers for video?
Most video codecs, such as H.264 and H.265, store colour at half the resolution and need the width and height to be divisible by 2. Some encoders even prefer multiples of 8 or 16. If an export fails or adds a thin black line, round the size to even numbers.
Frequently asked questions
What aspect ratio is 1920 × 1080?
1920 × 1080 is 16:9, the standard ratio for Full HD video, TV and most monitors. The same ratio applies to 1280 × 720, 2560 × 1440 and 3840 × 2160.
How do I keep the aspect ratio when resizing?
Enter the original size, then type only the new width or the new height. The other side is calculated from the ratio, so the picture keeps its shape.
What is the aspect ratio of a phone screen?
Modern phones are taller than 16:9, often around 19.5:9 or 20:9. Videos for stories, Reels and TikTok use 9:16, which is 1080 × 1920 pixels.
Is 16:10 the same as 8:5?
Yes. 16:10 simplifies to 8:5, but screen makers usually write 16:10 so it is easy to compare with 16:9.
Why does 1366 × 768 not give exactly 16:9?
1366 × 768 simplifies to 683:384, which is 0.05% wider than 16:9. Screen makers rounded the width to a convenient number, so it is treated as 16:9.
Are my images uploaded when I read their size?
No. The image is opened in your browser only to read its width and height. It is not uploaded or stored.
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