Type a width and height and read the reduced ratio (via GCD) plus its decimal value. Lock the ratio and edit either dimension — the other follows, rounded to whole pixels. Preset chips cover 16:9, 4:3, 21:9, 1:1, 9:16 and 3:2 with typical resolutions listed, and the fit/fill helper scales any source size into a target box both ways: contain and cover.
Privacy ledger
Data acquired
None.
Libraries used
Lit 3 — bundled into the tool file itself.
Data stored
None.
Data transmitted
None.
Use it on your own page
Download the tool as a single self-contained HTML file: readable source with the Lit library included, zero network requests — it works opened straight from your disk, and you can customize everything.