UniFi PoE Budget Planner
A switch does not spend its PoE budget on what your devices consume. It spends it on what their class reserves at the port, which is always the larger number — and it sheds ports, by a default policy rather than by what you care about, when the two finally disagree. This counts the real figure before the cold night that finds it.
Switch
400 W across 24 PoE ports, 60 W maximum on any one port, 802.3bt and below.
Powered devices
Reserved at the port
212.4Wof 400 W
53% — Inside the design rule, with room to grow.
- Devices consume
- 143.4 W
- Headroom to 80%
- 107.6 W
- Room for
- 3 more devices
- Ports used
- 10 of 24
| Device | Class | At the port | Reserved |
|---|---|---|---|
| 4 × UniFi U7 Pro | Class 4 | 30 W | 120 W |
| 6 × UniFi Protect G6 Bullet | Class 3 | 15.4 W | 92.4 W |
Budgets are spent at the port, not at the device: a Class 4 port reserves 30 W to guarantee 25.5 W at the far end, and the difference is the cable-loss allowance in the standard. Growth is counted in 30 W Class 4 additions against the 80% ceiling. Budgets never pool across chassis.
The arithmetic
A powered device signals a class during detection, and the switch allocates against that class rather than against whatever the device settles into drawing. Class 3 is 15.4 W at the port for 12.95 W at the device; Class 4 is 30 W at the port for 25.5 W. The gap is not a manufacturer hedge — it is the cable-loss allowance written into the IEEE standard.
Two constraints then apply independently, and clearing one does not clear the other. The total budget governs the sum of every port; the per-port limit governs the most any single port will deliver. A chassis with a generous total can still be the wrong one for a 60 W device, and eight Class 4 devices can consume a modest budget entirely while no single port is near its ceiling.
The pass mark here is 70 to 80 percent of the rated budget, not 100. The remaining margin absorbs seasonal heater draw, night-time infrared load, devices added after handover without a budget review, and the fact that a supply running flat out runs hotter and ages faster than one running at three-quarters.
Every switch, access point and camera offered above is read from the same spec records that render the switch lineup, each one sourced. The full reasoning — mixed port groups, shedding order, PoE as UPS load, and why budgets never pool across a stack — is in the PoE budget guide.
The UniFi Network application reports per-port draw and total consumption per switch, which turns all of this from an estimate into a measurement. Watch it across a full day and night before you trust it — including this — because infrared illuminators, heaters and evening client load all peak at predictable times a mid-afternoon reading will miss.