Aspect Ratio Calculator
An aspect ratio is a width divided by a height, reduced to its simplest form — so 1920×1080 becomes 16:9. Enter any two dimensions below and this calculator simplifies the ratio, shows it as a decimal and a percentage, and scales it to a new size without stretching.
Scale it, keeping this ratio
Matching height: —
Matching width: —
Scaled values are rounded to whole pixels when they land within 0.01 px of an integer; otherwise the exact figure is shown — a video encoder or design tool may round slightly differently.
Pick an image file and this page reads its real pixel dimensions on your device and fills them in above. The file is never uploaded anywhere.
The common ratios, each with its own calculator
16:9 calculator
Widescreen HD & 4K video. Used for: YouTube and streaming video, HDTV, most laptop and monitor panels, presentation slides.
9:16 calculator
Vertical phone video. Used for: TikTok, Instagram Reels, YouTube Shorts, Stories — anything shot or published for a phone held upright.
4:3 calculator
Classic screens & older cameras. Used for: Older TV and monitors, iPad screens (2048×1536 and similar), many compact and Micro Four Thirds cameras, classic presentation slides.
1:1 calculator
The square. Used for: Instagram square posts, profile pictures and avatars everywhere, product thumbnails, app icons.
21:9 calculator
Ultrawide — with an honest footnote. Used for: Ultrawide monitors, cinematic video, wide website hero banners.
4:5 calculator
Portrait posts that fill the feed. Used for: Instagram and Facebook portrait posts (1080×1350), Pinterest-style layouts, portrait photography crops.
How the maths works
To simplify a ratio, divide both the width and the height by their greatest common divisor (GCD) — the largest number that divides both. For 1920×1080 the GCD is 120: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, giving 16:9. To scale, keep the ratio fixed: new height = new width × (ratio height ÷ ratio width). So at 16:9, a width of 1280 needs a height of 1280 × 9 ÷ 16 = 720.
Two honest warnings. First, not every familiar-sounding pair is exact: 1366×768 laptop screens simplify to 683:384, which is close to 16:9 but not equal to it. Second, "21:9" ultrawide monitors are mostly not 21:9 at all — our 21:9 page shows what the common panels simplify to.
Frequently asked questions
What is the aspect ratio of 1920×1080?
16:9. Divide both numbers by their greatest common divisor (120) and you get 16 and 9. As a decimal it is 1.7778:1, and the height is 56.25% of the width.
How do I resize an image without distorting it?
Change the width and height by the same factor. If you double the width, double the height. Use the scaling boxes in the tool above: type the new width and it will tell you the matching height for the same ratio.
Does this site upload my image?
No. The image checker reads the file with your browser's own image loader and reports its pixel dimensions. Nothing leaves your device, and there is no server here to send it to.
Why does my image's ratio have big numbers, like 683:384?
Because the simplified form is whatever the GCD leaves behind. Camera sensors and screen panels often use dimensions that only look like a tidy ratio. 683:384 is the exact truth for 1366×768; "about 16:9" is the friendly lie.
What ratio should I use for YouTube, Instagram or print?
See the social media image sizes chart for platform slots, the screen resolution chart for 720p–8K displays, and photo print ratios for paper sizes.