An aspect ratio calculator is a free design tool that reduces any width and height to its simplest ratio (like 16:9) and scales dimensions proportionally. Enter your size, pick a preset, then type a new width or height to get the matching dimension without distortion.
Your dimensions
Common presets
Scale proportionally
Enter a new width or height - the other dimension is calculated to keep the same ratio.
How do you calculate aspect ratio?
Divide both dimensions by their greatest common divisor. For 1920x1080, the GCD is 120, giving 16:9. The calculator above does this instantly and draws a to-scale preview box, so you can verify the shape matches what you expect before exporting.
Ratios are written width:height, so 16:9 is landscape widescreen while 9:16 is the same shape rotated for portrait phone video.
What is 16:9 in pixels?
16:9 is a ratio, not a fixed size - common 16:9 resolutions include 1920x1080 (Full HD), 1280x720 (HD) and 3840x2160 (4K). Any width and height in the same 16:9 proportion display without distortion. Use the scaler above: enter one dimension and it computes the matching 16:9 partner.
For social video, 9:16 (1080x1920) is the vertical equivalent used by Reels, Shorts and TikTok.
How do I resize an image without stretching it?
Lock the aspect ratio and change only one dimension, letting the other scale proportionally. If you change width and height independently, the image stretches. Enter your current size above, type the new width (or height), and copy the calculated partner dimension into your editor or CSS.
- Enter your width and height, or pick a preset.
- Read the simplified ratio and check the visual preview.
- Type a new width or height in the scaler.
- Copy the calculated matching dimension.
Frequently asked questions
Is this aspect ratio calculator free?
Yes. Calculate unlimited ratios and scales with no account and no daily caps. Everything runs in your browser.
How is the ratio simplified?
Both dimensions are divided by their greatest common divisor. For example, 1920x1080 shares a GCD of 120, which simplifies to 16:9.
Can it handle portrait ratios like 9:16?
Yes. Enter any width and height and the tool simplifies them as-is, portrait or landscape, with a to-scale visual preview.
What is the difference between 16:9 and 4:3?
16:9 is the widescreen standard for video and modern displays; 4:3 is the older, squarer TV and monitor format. The presets let you jump between both instantly.
How do I use this with CSS?
Take the simplified ratio into the CSS aspect-ratio property, for example aspect-ratio: 16 / 9. The scaler gives you exact pixel pairs for fixed-size layouts.