Aspect ratio calculator
Original size on the left, the one new dimension you know on the right. The missing number keeps the proportions exact.
Scaled size
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—Simplified ratio
—Ratio (decimal)
Frequently asked questions
How is the missing dimension calculated?
Cross-multiplication: new height = new width x (original height / original width). A 1920x1080 video scaled to 1280 wide becomes 1280 x 720.
What are the common aspect ratios?
16:9 for video and monitors, 4:3 for older screens, 1:1 for square posts, 9:16 for phone-vertical (Stories, Shorts, Reels), 3:2 for most photos, and 21:9 for ultrawide.
Why does the simplified ratio sometimes look odd?
The simplifier reduces by the greatest common divisor, so 1366x768 reduces to 683:384 rather than a tidy 16:9, because it is not exactly 16:9. The decimal ratio shown alongside makes near-misses obvious.