These are the sizes the homepage opens on. Each link is that document’s own page: the print or upload size, the head-height rule where one is published, and the tool preset to it. Aadhaar’s page says what UIDAI actually prints — a 35 × 45 mm colour photograph — and does not invent a file-size limit.
SSC, UPSC, IBPS, SBI, NEET UG, JEE Main and RRB each have a page. The pixel size and the kilobyte range come from that exam’s notice. Where the notice does not state pixels, the page says so instead of guessing.
Requirements for 966 documents in 166 countries — passports, visas, residence permits, ID cards and licences. Each page sets out the size, head height and background, and opens the tool preset to that document. See every document.