Check a switch's PoE budget against connected devices using 802.3af, at and bt class limits, with cable loss included.
PoE standards define the power delivered by the sourcing equipment, and part of it is lost as heat in the cable before it reaches the device. Because most devices draw well under their class limit, the average figure sizes normal operation while the worst-case figure is what a full-load event demands. PoE budget exhaustion does not fail gracefully: the switch sheds power from the lowest-priority ports, and the cameras or access points that drop are rarely the ones you expected.
Power over Ethernet (PoE) Budget
required = devices × class limit × average draw share × (1 + cable loss); ports at full class = budget ÷ (class limit × loss factor).
required = devices × class limit × average draw share × (1 + cable loss); ports at full class = budget ÷ (class limit × loss factor). PoE standards define the power delivered by the sourcing equipment, and part of it is lost as heat in the cable before it reaches the device. Because most devices draw well under their class limit, the average figure sizes normal operation while the worst-case figure is what a full-load event demands.
PoE budget exhaustion does not fail gracefully: the switch sheds power from the lowest-priority ports, and the cameras or access points that drop are rarely the ones you expected.
This calculator takes 5 inputs: Switch PoE budget, Powered devices, PoE standard per port, Average draw as a share of the class limit, Cable dissipation loss. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.