This is the commonly used size: we found no requirement published by the institution. Confirm it before your application.
Tips to get it right the first time
Scan the original document in colour, clearly: UIDAI rejects blurred or cropped scans.
Online you can update only your address and documents; biometrics, mobile and photo need an Aadhaar centre.
The name and date of birth on the proof must match your Aadhaar.
How to do it with Requisito Listo
Open «Aadhaar document update (myAadhaar)».
Scan the pages with the camera or pick a PDF or photos you already have.
Put the pages in order.
The app builds the PDF under the size the portal asks for.
At the end you'll see a checklist: size, file weight, background and format. If something doesn't comply, it tells you what to fix before the portal rejects it.