Percentages and pixels
A percentage applies to both sides, so 50% gives a quarter of the pixels and 200% four times as many. Output dimensions are rounded to whole pixels, which can nudge the aspect ratio by a fraction of a pixel; the readout shows the result before you commit.
Use the Pixels mode instead if you need an exact width or height, or Long edge if you need a maximum size for a website or upload form.
Questions
What percentage makes a picture half the size?
50% halves both width and height (a quarter of the area). To halve the area, scale to 70.7%.
Can I go above 100%?
Yes, up to 1600% on either side, within the 100 megapixel output limit. Above 200%, consider the AI engine for detail.
Can I scale many pictures by the same percentage?
Yes — Bulk scale images applies one percentage (or any other size rule) to a whole set and saves a ZIP.
Is my picture uploaded anywhere?
No. Decoding, scaling and encoding all run in this browser tab, and the scaling engine runs in a Web Worker with no network code in it. The only download the site can make for you is an AI model file, and only after you press the button that names its size — that request contains no picture.