Aspect Ratio Calculator
Enter the original width × height; change just one new dimension and the other auto-scales while keeping the ratio. Use it for resizing video, images, and web layouts.
Original
New size
How to Use
Type the original width × height in pixels (or any unit). The preset buttons fill in common ratios: 16:9, 4:3, 1:1, 9:16, etc.
In the "New size" area, edit just the width or just the height — the other auto-recalculates to keep the original ratio.
The simplified ratio (16:9), decimal ratio (1.778), and a preview rectangle are shown. The "WxH" text can be copied with one click.
FAQ
Why do 16:9 and 4:3 matter?
TVs, monitors, phones, video content, and social posts each have recommended ratios — 16:9 (HD/4K), 9:16 (Reels/Shorts), 1:1 (Instagram square), 4:3 (older TVs/iPads), 21:9 (cinematic). Off-ratio media gets cropped or letterboxed.
How is the ratio simplified?
Take the GCD of width and height, divide both. 1920×1080 → both ÷120 = 16:9. If the simplified ratio is unwieldy (e.g., 1366×768 → 683:384), the closest standard ratio is shown as "≈ 16:9".
How to read the decimal ratio (1.778)?
It's width ÷ height. 16/9 = 1.778, 4/3 = 1.333, 1/1 = 1.0, 9/16 = 0.5625 (vertical). Use it directly in design tools that take a "ratio lock" value.
I see fractional pixels.
Calculated dimensions are rounded to integers. e.g., resizing 1280×720 to width 1000 gives height 562.5 → 563. A 1-pixel difference is well under 0.1% of the original ratio and visually negligible.
Is anything sent to a server?
No. All calculations run in your browser; nothing leaves the page.
