PoE power budget calculator for your switch

A Power over Ethernet switch has a total power budget, and that number is usually smaller than the sum of its ports. A 48-port switch that lists 370 watts cannot give every port its maximum. If you add devices until you pass the budget, some will not power up or will reboot at random.

List your devices below with a count and the watts each one needs at the switch port. The calculator adds them up, compares the total to the switch budget, and shows what is left. It flags you when you are past 80 percent so you keep headroom.

How the math works

• Draw for each line is the count times the watts per device.
• Total draw is the sum. Headroom is the budget minus the total, and utilization is total divided by budget.

Use the figure from the device's data sheet, measured at the switch port. The standards set per-port ceilings at the switch: about 15.4 W for 802.3af, 30 W for 802.3at and 60 W or 90 W for 802.3bt. Many devices draw less than the ceiling, but cameras with heaters and some access points can spike, so add margin.

Worked example

A switch has a 370 W budget. You plan 10 phones at 7 W, 4 access points at 15.4 W and 6 cameras at 12 W. That is 70 + 61.6 + 72 = 203.6 W, or about 55 percent of the budget, with 166.4 W left. Adding eight 30 W devices later would take you to 443.6 W, which is over budget.