Aspect Ratio Calculator: Find Ratio, Width and Height
Enter any width and height and see the aspect ratio at once, or enter a ratio and one side and get the missing size. This free aspect ratio calculator simplifies dimensions such as 1920 by 1080 to 16:9, scales images, videos and screens up or down without stretching them, and shows a live preview of the shape. It works for photos, video, monitors, social posts, prints and web design, and it runs in your browser with no upload.
Use it to resize an image to fit a layout, find a video size for YouTube or Instagram, check what ratio your screen has, or work out how much to crop a photo to reach a new shape.
Use the toolSame ratio, other sizes
Find the ratio
1920 by 1080 becomes 16:9, with a live preview.
Find a missing side
Pick a ratio, enter the width or the height.
Crop helper
Crop size, start point and a padding option.
Private by design
Only numbers are used. No image is uploaded.
Type a width and a height to see the simplified ratio, or choose a ratio and one side to get the other. The crop helper shows how much to remove to reach a new shape without stretching.
Key Takeaways
- An aspect ratio compares width to height, so 1280 by 720 and 3840 by 2160 are both 16:9.
- To find a missing side, divide by one ratio number and multiply by the other.
- Changing both sides to numbers that only look right causes slight stretching. Change one side and let the other follow.
- To reach a new shape, crop (remove part of the picture) or pad (add background). Both keep the proportions.
- The calculator works only with numbers. No image is uploaded.
How to Use the Aspect Ratio Calculator
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1STEP 1 Choose a mode. To find the ratio of an image or screen, enter its width and height.
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2STEP 2 To find a missing side, pick a ratio from the presets or type your own, then enter either the width or the height.
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3STEP 3 The result appears instantly, with a preview so you can see the shape.
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4STEP 4 Use the crop helper if you want to change an existing picture to a new ratio without distortion.
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5STEP 5 Copy the result and use it in your editor, design tool or code.
What Is an Aspect Ratio?
An aspect ratio describes the shape of a rectangle by comparing its width to its height. It is written as two numbers with a colon, such as 16:9, which means that for every 16 units of width there are 9 units of height. The ratio does not say how big something is. A 1280 by 720 image and a 3840 by 2160 image are very different in size, but both are 16:9.
Keeping the same aspect ratio when you resize means the picture is scaled evenly, so circles stay round and faces are not stretched or squashed.
How to Calculate Aspect Ratio
You can work out the ratio by hand in three steps:
- 1Write the width and height as a fraction, for example 1920 over 1080.
- 2Find the greatest common divisor, the biggest number that divides both. For 1920 and 1080 it is 120.
- 3Divide both sides by it: 1920 divided by 120 is 16 and 1080 divided by 120 is 9. The aspect ratio is 16:9.
To find a missing side, use the formula height = width divided by ratio width, times ratio height. For a 4:3 picture that is 1000 pixels wide, the height is 1000 divided by 4, times 3, which is 750 pixels. To find a width from a height, use width = height divided by ratio height, times ratio width.
Worked examples
| Known | Ratio | Result |
|---|---|---|
| Width 1280 | 16:9 | Height 720 |
| Width 1000 | 4:3 | Height 750 |
| Width 1080 | 4:5 | Height 1350 |
| Height 1080 | 16:9 | Width 1920 |
| Height 600 | 3:2 | Width 900 |
| Width 800 | 1:1 | Height 800 |
Common Aspect Ratios and Where They Are Used
| Ratio | Where you see it | Example size |
|---|---|---|
| 16:9 | HD and 4K video, YouTube, most TVs and monitors, presentations | 1920 x 1080 |
| 4:3 | Older TVs and monitors, many tablets, some compact cameras, slides | 1024 x 768 |
| 3:2 | 35mm film and many DSLR and mirrorless photos, some laptops | 3000 x 2000 |
| 1:1 | Square social posts, profile pictures, album covers | 1080 x 1080 |
| 4:5 | Portrait posts on social apps | 1080 x 1350 |
| 9:16 | Vertical video such as stories, reels and shorts | 1080 x 1920 |
| 21:9 | Ultrawide monitors and wide movie formats | 2560 x 1080 |
| 2:3 | Portrait photos and posters | 2000 x 3000 |
| 16:10 | Some laptops and monitors | 1920 x 1200 |
| 1:1.414 | A paper sizes (A4, A3 and so on), which keep the same shape when halved | 210 x 297 mm for A4 |
Aspect Ratio of Common Resolutions
Here are the ratios for popular pixel sizes. Many different resolutions share one ratio, so you can scale between them safely.
| Width x height | Aspect ratio | Common use |
|---|---|---|
| 1920 x 1080 | 16:9 | Full HD video and monitors |
| 1280 x 720 | 16:9 | HD video, YouTube 720p |
| 3840 x 2160 | 16:9 | 4K UHD TVs and video |
| 1080 x 1080 | 1:1 | Square social posts |
| 1080 x 1350 | 4:5 | Portrait social posts |
| 1080 x 1920 | 9:16 | Vertical video, stories and reels |
| 1200 x 630 | 40:21 (about 1.91:1) | Link preview images |
| 1024 x 768 | 4:3 | Older monitors and iPad screens |
| 1600 x 1200 | 4:3 | Older 4:3 monitors |
| 3000 x 2000 | 3:2 | DSLR photos |
| 2560 x 1080 | 64:27 (sold as 21:9) | Ultrawide monitors |
| 1920 x 1200 | 8:5 (also called 16:10) | Some laptops and monitors |
Aspect Ratio for Video: YouTube, Instagram, TikTok
Platforms are built around certain shapes. Standard YouTube videos are 16:9 and play with no black bars at that shape. Vertical short form video, such as stories, reels and shorts, is designed for 9:16. Social feed posts commonly use 1:1 or 4:5. Platforms change their supported sizes from time to time, so check the current guidelines of the platform before you export. Match the ratio first, then pick the pixel size to suit the quality you need.
How to Resize an Image Without Distorting It
- Keep the ratio locked. Change only one side and let the other follow.
- If the new shape must be different, crop instead of stretching. Cropping removes part of the picture but keeps the proportions of what remains.
- Or pad. Add a background colour or blur on the sides so the whole picture fits inside the new shape.
- Do not scale up too far. Enlarging a small image makes it soft, even if the ratio is right.
Crop to a new ratio: example
You have a 4000 by 3000 photo (4:3) and want 16:9. Keep the full width of 4000 and work out the new height: 4000 divided by 16, times 9, equals 2250. You will crop the height from 3000 to 2250 pixels, which removes 750 pixels in total, for example 375 from the top and bottom. The crop helper does this for any size and ratio.
Aspect Ratio for Print and Screens
For prints, the same idea applies with centimetres or inches. A photo at 3:2 will not fit a 4:5 frame without cropping, which is why prints sometimes cut off the edges of a picture. For screens, a 16:9 monitor shows a 4:3 video with bars at the sides, and shows an ultrawide video with bars at the top and bottom. Knowing the ratios in advance helps you pick the right frame, crop or canvas size.
Common Aspect Ratio Mistakes
- Resizing by changing both sides to numbers that look right. A small mismatch in ratio causes a slight stretch you may not notice until later.
- Mixing up orientation. 16:9 is landscape and 9:16 is portrait. Use the swap button to flip it.
- Rounding too early. If the result is not a whole number, round only the final pixel value.
- Forgetting that screens and print use different shapes. Check the target before you design.
Is the Aspect Ratio Calculator Private?
Yes. All calculations happen in your browser. Your numbers are not sent to a server and no image is uploaded. The calculator works with sizes, not with the picture itself.
More Free Image and Design Tools
Once you know your size, resize the picture with the Image Resizer. Need other quick helpers? Try the Barcode Generator, or use the Word Counter for captions and descriptions, and the Case Converter for tidy titles.
FAQs
How do I calculate the aspect ratio of an image?
Divide the width and the height by their greatest common divisor. For a 1920 by 1080 image, both numbers divide by 120, which gives 16 and 9, so the ratio is 16:9. You can also type the width and height into the calculator and it simplifies them for you instantly, with a preview of the shape.
How do I find the height from a width and aspect ratio?
Divide the width by the ratio width and multiply by the ratio height. For a 1280 pixel wide image at 16:9, divide by 16 to get 80, then multiply by 9 to get 720 pixels. The calculator does this in one step and can work the other way to find a width from a height.
What is the aspect ratio of 1920x1080?
1920 by 1080 is 16:9. This is the shape of Full HD video, most modern monitors and TVs, and YouTube videos. Other resolutions with the same ratio include 1280 by 720, 2560 by 1440 and 3840 by 2160, so you can scale between them without stretching the picture.
What is the best aspect ratio for Instagram and YouTube?
YouTube standard videos use 16:9. Instagram feed posts commonly use 1:1 or 4:5, and stories and reels use 9:16. Platforms update their guidance from time to time, so check the current requirements before you upload. Match the ratio first, then choose a pixel size that gives good quality.
How do I change the aspect ratio without stretching an image?
You have two choices: crop or pad. Cropping cuts away part of the picture to reach the new shape, and padding adds space or background so the whole picture fits. Stretching both sides to new numbers distorts the image, so choose a method that keeps the original proportions.
Does the calculator work for video?
Yes. Aspect ratio works the same way for photos, video, screens and print. Enter the video width and height, or choose a ratio such as 16:9 or 9:16 and enter one side. It is useful for planning exports, setting up an editing timeline and checking how a clip will fit a platform.
What does 16:9 mean?
16:9 means that for every 16 units of width, the shape is 9 units tall. It is a wide landscape shape, about 1.78 times wider than it is tall. It became the standard for HD television, video and monitors, and it is the most common ratio you will find on screens today.
Is my data uploaded when I use the calculator?
No. The calculator runs in your browser and works only with the numbers you type. It does not send them to a server or store them, and it does not need to receive an image. You can use it for private projects, client work and unreleased designs without any account.
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