16:9 Aspect Ratio Calculator
Calculate the missing side for any aspect ratio — 16:9, 4:3, 21:9, 1:1 or custom — or simplify the ratio of two known dimensions.
Processed entirely in your browser — nothing you enter here is ever uploaded.
Result
About this tool
This page opens the aspect ratio calculator with 16:9 already selected — type the width or the height you know and the matching side is computed for you.
16:9 is the default shape of the modern screen: YouTube players, Full HD (1920 × 1080), QHD (2560 × 1440) and 4K UHD (3840 × 2160) monitors, TVs, and landscape video on every major platform all use it. Whenever you resize a video frame, a thumbnail or a presentation slide, this is almost always the ratio to keep.
The full tool also covers 4:3, 21:9, 1:1 and any custom ratio, and can simplify two known dimensions back to their ratio. Every calculation happens locally in your browser — nothing you enter is sent anywhere.
Example. A width of 1920 at 16:9 returns 1920 × 1080.
Limit. Displayed numbers keep at most two fraction digits, and a ratio is simplified from at most six decimal places of the typed sides.