Aspect Ratio Calculator
Aspect ratio calculator — enter a width and height to get the simplified aspect ratio (like 16:9), then enter a new width or height to find the matching dimension that keeps the same ratio. Perfect for images, video and screens. Runs in your browser.
Aspect Ratio Calculator
Resize — fill ONE to find the other
How to Use the Aspect Ratio Calculator
Enter original size
Type the current width and height.
Read the ratio
See it simplified, e.g. 16:9.
Enter a new size
Fill the new width OR height.
Get the match
The other dimension keeps the ratio.
Resize Without the Squash
Aspect ratio is the shape of an image, video or screen — the proportion of its width to its height — and getting it wrong is why pictures end up stretched, faces look squashed, and videos appear with unexpected black bars. This calculator does the two jobs that matter: it simplifies any width and height into a clean ratio like 16:9, and it resizes a dimension while holding that ratio constant, so you can scale content up or down without distorting it. Enter the original size to see the ratio, then enter a new width or height and it returns the matching dimension.
Simplifying the ratio uses the same greatest-common-divisor method as reducing a fraction: 1920 by 1080 both divide by 120 to give 16:9, and 1024 by 768 both divide by 256 to give 4:3. The calculator also shows the decimal form — width divided by height — which is a single number that makes ratios easy to compare: 16:9 is about 1.78, 4:3 is about 1.33, and a perfect square is exactly 1. Knowing the decimal is useful when a piece of software asks for a ratio as one value rather than two.
The resize function is where the practical value lies. Stretching happens when you force content into a different aspect ratio than it started with — squeezing a 16:9 video into a 4:3 frame compresses everything horizontally. To avoid that, you keep the ratio: type the new width you need and the tool gives the height that preserves the proportions, or fix the height to get the width. When you genuinely need to change the shape, the distortion-free alternatives are cropping (cutting to the new ratio) or boxing (letterboxing adds bars top and bottom, pillarboxing adds them at the sides). The common ratios are worth memorising — 16:9 for modern video and screens, 9:16 for vertical Stories and Reels, 1:1 for square posts, 3:2 for classic photography, 21:9 for ultrawide — because matching your export to the target ratio is what keeps everything looking right. The unit does not matter, only the proportion, and as with every RECATOOLS tool, the calculation runs entirely in your browser.
Scale, don’t stretch: keep the aspect ratio constant and circles stay round — change the ratio only by cropping or boxing.
10 Facts About Aspect Ratios
16:9 is the standard for HD and 4K video.
4:3 was the old TV and monitor standard.
1:1 is the square format popular on social media.
21:9 is ultrawide cinema and monitors.
Resize keeping the ratio to avoid stretching.
A 9:16 ratio is vertical video (Stories, Reels).
The ratio simplifies via the greatest common divisor.
3:2 is a classic photography ratio (35 mm).
Letterboxing fits a wide image on a narrower screen.
This calculator runs in your browser — nothing is uploaded.
Frequently Asked Questions
- An aspect ratio describes the proportional relationship between an image or screen’s width and its height, written as two numbers separated by a colon, such as 16:9. It tells you the shape regardless of the actual size, so a 16:9 image looks the same whether it is a phone thumbnail or a cinema screen. This calculator simplifies any width and height into that form.
- By dividing the width and height by their greatest common divisor — the largest number that divides both evenly. A 1920 by 1080 image divides by 120 to give 16:9; a 1024 by 768 image divides by 256 to give 4:3. The calculator finds that divisor for you and shows the lowest-terms ratio plus the decimal equivalent.
- Keep the aspect ratio constant. Enter the original width and height, then type the new width you want, and the calculator gives the matching height that preserves the ratio (or the matching width if you fix the height). Following that figure means your image or video is scaled, not stretched, so circles stay round and faces stay natural.
- The most common are 16:9 (HD and 4K video, modern screens), 4:3 (older TVs and monitors), 1:1 (square social posts), 9:16 (vertical video like Stories and Reels), 3:2 (classic 35 mm photography), and 21:9 (ultrawide cinema and monitors). Knowing which you are targeting helps you crop and export correctly.
- It is the width divided by the height — a single number that captures the ratio. A 16:9 ratio has a decimal of about 1.78, a 4:3 ratio about 1.33, and a square is exactly 1. The decimal is handy for comparing two ratios quickly or for tools that ask for a single ratio value.
- Because it was resized to a different aspect ratio than the original, forcing the pixels to distort. If you scale a 16:9 image into a 4:3 box without cropping, everything is squashed horizontally. The fix is either to keep the original ratio when resizing, or to crop the image to the new ratio before scaling.
- They are ways to fit content of one aspect ratio onto a screen of another without distortion. Letterboxing adds black bars top and bottom to show a wide image on a narrower screen; pillarboxing adds bars on the sides to show a narrow image on a wider screen. Both preserve the original ratio rather than stretching the picture.
- Yes — enter any width and height in pixels, centimetres or any unit, and it simplifies the ratio and scales dimensions proportionally. The unit does not matter as long as both numbers use the same one, because aspect ratio is purely about proportion.
- The ratio simplification and the proportional scaling are exact. When scaling produces a fractional pixel dimension, the calculator shows the precise value; you would round to the nearest whole pixel when actually exporting, which is normal and visually imperceptible.
- Completely free, with no account or limit. It works offline once the page has loaded and collects no data.
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