I always use the school's Cost of Attendance for Room & Board for off campus housing. That's what's recommended here too https://www.fidelity.com/learning-center/personal-finance/college-planning/college-529-spending
Pay attention to the info about the AOTC credit too.
This is way oversimplified but here's the basics:
School Cost of Attendance (Annual # so you have to split into quarters or semesters) for Room and Board and fees
subtract Health Fee, sports fee,etc
books - adjust amount from cost of attendance as needed
subtract scholarship $ received
subtract amount you want to leave for AOTC tuition if eligible.
add in - computer expense
add in - justifiable extra expense like extra lab $ or other class fees
That's the amount to disburse from the 529.