Count powered devices separately
Total switch ports and PoE ports are not the same. Write down every camera, access point, bridge, phone, or controller that needs power from Ethernet.
Check per-port and total budget
A switch can advertise 30W per port while still having a total budget that cannot run every port at max draw.
Leave startup and cold-weather headroom
Cameras with IR, PTZ motors, heaters, or long cable runs may draw more at certain times. Leave headroom rather than matching the budget exactly.
Plan priority before an overload
If the switch sheds lower-priority ports when the budget is exceeded, decide which cameras or APs should stay powered first.