宽高比调整器（图片、视频、社交媒体）

计算原理

Two modes share one underlying calculation. Ratio = original width ÷ original height, and the Calculate ratio from dimensions mode reduces that to its simplest integer form using the greatest common divisor, turning 1920 × 1080 into 16:9. Resize keeping ratio applies it instead: with Lock width, new height = new width ÷ ratio; with Lock height, new width = new height × ratio. The other field updates as you type, and a dashed preview box redraws to the resulting shape.

The Lock dropdown decides which field you drive, though the tool also tracks whichever of the two new-dimension fields you edited last and follows that. The eight presets — 1:1 square, 4:3, 16:9 HD, 21:9 ultrawide, 9:16 vertical, 4:5 IG portrait, 1.91:1 FB / link and 2:3 Pinterest — work by keeping your original width and rewriting the original height to match the chosen ratio, then copying both values into the new fields.

The results are purely geometric: you get the dimensions that preserve proportion, not guidance on how to crop or letterbox an image that is already the wrong shape. Displayed values are rounded, so a ratio such as 21:9 can land half a pixel off and produce a one-pixel discrepancy in real output. Non-integer original dimensions are rounded before the greatest common divisor runs, which makes the simplified ratio approximate for those.

常见问题