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
Upload one proof of identity and two proofs of California residency.
Save your confirmation code: you need it at the DMV office.
Bring the originals of everything you uploaded to your appointment.
How to do it with Requisito Listo
Open «California REAL ID: document uploads».
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.