PoE Budget Calculator

Adds up how much of a switch's total PoE power budget a list of connected devices actually needs, so you find out whether you're over budget before the ninth access point refuses to power up, not after.

Why "the switch has 48 PoE ports" doesn't mean 48 devices at full power

A switch's PoE budget is a shared pool, not a per-port guarantee. A 48-port PoE+ switch commonly has a total budget well under what 48 ports at full 30W each would need (that would be 1,440W — most switches in this class budget somewhere around 370–740W total). The switch is betting, correctly, that not every port will demand maximum power simultaneously — but if you actually do connect 48 power-hungry PTZ cameras, you can genuinely run out of shared budget well before you run out of physical ports.

What the switch actually has to supply, vs. what the device receives

The wattage classes here — 15.4W, 30W, 60W, 90W — are what the switch port has to budget, not what the device actually receives. Resistive loss in the Ethernet cable itself eats several watts along the way, more on longer runs, which is exactly why 802.3af devices are rated to actually use up to about 12.95W while the switch budgets 15.4W for that port — the difference is cable loss the standard already accounts for. Budgeting for what the switch allocates per port, not what the device consumes, is the number that actually determines whether you're within total switch capacity.

Matching the standard to what you're actually deploying

• 802.3af (PoE) — basic IP phones, older or basic access points
• 802.3at (PoE+) — most current Wi-Fi 6 access points, PTZ cameras
• 802.3bt Type 3/4 (PoE++) — Wi-Fi 6E/7 APs, thin clients, small PoE-powered displays — genuinely high-draw devices that older standards can't power at all

Headroom is worth planning for, not just meeting exactly

Sitting right at 100% of budget leaves no room for adding a device later without either upgrading the switch or physically moving something to a different one — an annoying, avoidable position to be in six months after the install. It's also worth knowing some switches derate their total PoE budget at high ambient temperature, which matters more than people expect in a poorly-ventilated comms cabinet running warmer than the switch's rated environment — one more reason not to plan right up to the stated limit.