4:3 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 4:3 preselected — enter the width or the height and the other side appears at the classic ratio.
4:3 ruled screens for decades: standard-definition television, early computer monitors like 640 × 480 and 1024 × 768, most compact-camera photos and many document scanners. It is still everywhere today — iPad displays, Micro Four Thirds cameras and retro-styled game footage all keep the squarer 4:3 frame.
Beyond this preset, the full calculator handles 16:9, 21:9, 1:1 and any custom ratio, and simplifies any two dimensions you already have. All the math runs privately in your browser with no upload.
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.