Edit any two of width, height, or ratio. The tool locks the most recently edited field and solves for the unedited one. Ratio accepts forms like "16:9" or "1.7778".
Tip: enter width and height to read the ratio, or pick a preset and type one dimension to get the other. Aspect ratios like 16:9 always render identically regardless of scale — the browser just computes the other side.