Aspect Ratio Calculator
Resize while keeping proportions, and find the ratio of any size.
About this aspect ratio calculator
Enter the original width and height, then fill in either the new width or the new height โ the other is worked out for you, keeping the proportions identical. The panel underneath names the ratio, gives it as a decimal, and shows a scaled preview of the shape.
Presets cover the sizes people actually need: YouTube thumbnails, Instagram posts and stories, Facebook and LinkedIn banners, Open Graph cards, 4K, and A4 at print resolution.
What the common ratios are for
16:9 is HD video and nearly every modern screen. 9:16 is its vertical twin โ Reels, Shorts, TikTok, Stories. 1:1 is the square Instagram made ubiquitous, and 4:5 is the tallest the Instagram feed allows, which is why it takes up the most screen space.
3:2 is 35mm film and most DSLRs; 4:3 is classic television and most compact cameras; 21:9 is ultrawide monitors and anamorphic cinema. Print sizes are their own world: 4ร6 inches is 3:2, but 5ร7 and 8ร10 are not, which is why a photo printed at two sizes gets cropped differently.
Why 1366ร768 isn't quite 16:9
True 16:9 at 768 pixels tall would be 1365.33 wide, and you cannot have a third of a pixel โ so panel makers rounded up to 1366. The real ratio is 1.7786:1 rather than 1.7778:1: close enough that nobody notices, far enough that the fraction refuses to simplify to anything readable. That is why this calculator falls back to a decimal when the reduced fraction stops being useful.
Keeping the ratio identical when you resize is what stops an image looking stretched. If you need a genuinely different shape, crop rather than scale โ throwing pixels away looks correct, squashing them does not. The image cropper does exactly that, and the image resizer handles the scaling once the shape is right.
Frequently asked questions
How do I keep the aspect ratio when resizing an image?
Enter the original width and height, then type only the new width or only the new height. The other dimension is calculated so the proportions stay identical.
What is 1920ร1080 as an aspect ratio?
16:9. Both numbers divide by 120, giving 16 and 9 โ the standard HD video ratio.
What aspect ratio is an Instagram post?
1:1 square at 1080ร1080, or 4:5 portrait at 1080ร1350, which is the tallest the feed allows. Stories and Reels are 9:16 at 1080ร1920.
Why does my photo get cropped when I print it?
Print sizes have different ratios. A 3:2 photo from a DSLR fits a 4ร6 print exactly but must be cropped for 5ร7 or 8ร10, which are different shapes.
What is the difference between cropping and scaling?
Scaling changes the size and keeps everything in frame; cropping cuts part of the image away. To change the shape without distortion you must crop, not scale.