How to use the aspect ratio calculator
- In section 1, type the width and height of your image, video or screen. The simplified ratio, such as 16:9, appears at once together with the decimal value and a note if it matches a well-known format.
- In section 2, type a new width to get the matching height (or the other way around). Choose a preset ratio chip if you want to work with a standard format instead.
- In section 3, enter the size of a picture and choose a target ratio to see how much a crop removes and which pixels remain.
- In section 4, press Calculate next to a common platform size to load it into the ratio finder.
A calculator for designers, editors, photographers and developers
An aspect ratio is the proportional relationship between the width and the height of a rectangle. It is written as two numbers separated by a colon, and it does not depend on the actual pixel size: a 1280 by 720 video and a 3840 by 2160 video are both 16:9. Knowing the ratio matters whenever something has to fit a frame: uploading a video, designing a banner, printing a photo, choosing a monitor or setting the size of an embedded player on a web page.
Doing the arithmetic by hand is easy until it is not. Is 2560 by 1080 21:9? What height goes with a 1000-pixel-wide 4:5 image? How much of a 4000 by 3000 photo disappears when you crop it for Instagram? This calculator answers these questions instantly, shows a live drawing of the shape and keeps your numbers on your own device.
Common aspect ratios and where they are used
| Ratio | Decimal | Typical use |
|---|---|---|
| 16:9 | 1.78 | HD and 4K video, YouTube, TVs, most monitors |
| 4:3 | 1.33 | Older TVs, classic slides, many tablets and compact cameras |
| 1:1 | 1.00 | Square social posts, profile pictures, album covers |
| 9:16 | 0.56 | Stories, Reels, TikTok and YouTube Shorts |
| 4:5 | 0.80 | Instagram portrait posts |
| 3:2 | 1.50 | 35 mm film and most DSLR and mirrorless cameras |
| 21:9 | 2.33 | Ultrawide monitors and cinematic video |
| 16:10 | 1.60 | Many laptops and productivity displays |
Keeping proportions when you resize
Distortion happens when width and height are changed by different factors. A face stretched sideways or a logo squashed from the top is almost always a ratio mistake. The rule is simple: multiply or divide both dimensions by the same number. If you only know one target dimension, the other one follows from the ratio. For a 16:9 picture that must be 1000 pixels wide, the height is 1000 times 9 divided by 16, which is 562.5. Because images need whole pixels you round to 562 or 563, and the calculator shows both the exact and the rounded value.
When the original and the target ratios differ, you have to choose between three options: crop away part of the image, add bars or padding to fill the frame, or stretch it, which is rarely acceptable. Section 3 of the tool helps with the first two choices by calculating the cropped size and the padded canvas size side by side.
Cropping to a new aspect ratio
Suppose you have a 4000 by 3000 photo, which is 4:3, and you want a 4:5 portrait for Instagram. Because 4:5 is narrower, you must remove width. The largest 4:5 area that fits in the photo is 2400 by 3000 pixels, so 1600 pixels of the width, or 40 percent, are lost, 800 from each side if you crop in the centre. The calculator displays this result, the starting coordinates for the crop and a diagram with the remaining area dashed. If you do not want to lose any of the picture, the same section gives the canvas size you would need, in this case 4000 by 5000 pixels with 2000 pixels of padding in total at top and bottom.
Before cropping, think about the subject. Faces, products and text near the edge may be cut, so you may prefer an off-centre crop. Use the starting coordinates as a reference and shift them by hand. After cropping, you can shrink the file with our Resize Image and Compress Image tools.
Typical video and social media sizes
The table in section 4 lists widely used sizes, such as 1920 by 1080 for Full HD video, 1080 by 1350 for Instagram portrait posts and 1200 by 630 for link previews. They are useful starting points, but platforms change their recommendations. Treat the table as a quick reference, and check the current help page of the platform when publishing something important. If your file has the right ratio, the platform will scale it to the right size on its own, so the ratio matters more than the exact pixel count.
Aspect ratio and screens
When you compare monitors, the ratio shows the shape of the display, while the resolution shows its sharpness. A 27-inch 16:9 monitor and a 27-inch 21:9 monitor are the same diagonal size but very different shapes: the ultrawide is wider and shorter. If you watch 16:9 video on an ultrawide screen, you get black bars at the left and right; for a 4:3 clip on a 16:9 TV you get bars as well. Knowing the ratio before you buy or export avoids both surprises.
Tips and good practice
- Shoot or design a little wider than you need, so there is room to crop to several ratios later.
- Keep important content in the central 80 percent of the frame; edges are most likely to be cut.
- For the web, define the ratio in CSS with the aspect-ratio property, so the layout does not jump while images load.
- Export at the largest size you need and scale down, never up; enlarging a small image makes it blurry.
- Keep the ratio of original files, and produce cropped copies for each platform.
Private by design
This is a calculator, so it only works with the numbers you type. Nothing is uploaded, no cookies track you and no sign-up is needed. After the first visit it also works offline.
Frequently asked questions
How do I calculate an aspect ratio?
Divide both the width and the height by their greatest common divisor. For 1920 by 1080 the divisor is 120, which gives 16 and 9, so the ratio is 16:9. The calculator does this for you and also shows the decimal value (1.78 for 16:9) and whether the shape is landscape, portrait or square.
How do I resize an image without stretching it?
Keep the ratio fixed and change only one dimension. New height equals new width times original height divided by original width. In section 2, type the new width and the matching height appears. Enter exactly that pair in your image editor or video software to avoid distortion.
What is the difference between 16:9 and 16:10?
16:9 is the standard for TVs, monitors and online video. 16:10 is slightly taller and common on laptops, giving more vertical room for documents and code. A 16:9 video shown on a 16:10 screen has thin black bars at the top and bottom.
What aspect ratio should I use for Instagram, TikTok or YouTube?
Common choices are 1:1 or 4:5 for Instagram feed posts, 9:16 for Stories, Reels, TikTok and YouTube Shorts, and 16:9 for regular YouTube videos. Platforms update their guidelines, so confirm the current recommendation before you export.
What does the crop calculation tell me?
It shows how many pixels you must remove from the width or the height to reach the target ratio, the size that remains after a centered crop, the crop starting point, and the canvas size you would need if you wanted to add padding instead of cropping.
Why are some results marked with an approximate sign?
When a ratio does not scale to whole pixels, for example 16:9 at a width of 1000, the exact height is 562.5. The tool shows the exact value and a rounded pixel size. Most editors need whole numbers, so choose a width that divides evenly when you can.
Is 1.91:1 exactly 1200 by 630?
Not quite: 1200 divided by 630 is 1.905, which is close to 1.91:1. It is the size widely used for link preview and social share images. The calculator labels it as approximately 1.91:1.
Are my numbers sent anywhere?
No. The calculations are performed in your browser by JavaScript. Nothing is uploaded or stored, and the page also works offline after the first visit.
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