PoE power budget calculator
Ceiling mics, PTZ cameras, touch panels and Dante gear all want power from the switch. Add them up before you find out the hard way.
| Device | Qty | PoE class | Actual draw (W, optional) |
|---|
Devices
–
Power needed
–
Headroom left
–
PoE classes
| Class | Standard | At the switch port | At the device |
|---|---|---|---|
| 1 | 802.3af (PoE) | 4.0 W | 3.84 W |
| 2 | 802.3af (PoE) | 7.0 W | 6.49 W |
| 0 or 3 | 802.3af (PoE) | 15.4 W | 12.95 W |
| 4 | 802.3at (PoE+) | 30 W | 25.5 W |
| 5 | 802.3bt Type 3 | 45 W | 40 W |
| 6 | 802.3bt Type 3 | 60 W | 51 W |
| 7 | 802.3bt Type 4 | 75 W | 62 W |
| 8 | 802.3bt Type 4 | 90 W | 71.3 W |
The gap between the two columns is the worst-case loss in 100 m of cable.
How it works
A switch has a total PoE budget, separate from how many ports it has. Many switches reserve each port's full class maximum when a device connects, whether or not the device uses it. Others allocate by what the device reports over LLDP, or by measured draw. The calculator does it either way: by class, or by the actual watts you enter.
Field notes
- Read the switch's PoE budget, not its port count. A 24-port PoE+ switch often can't power 24 PoE+ devices at full load. Its total budget is the limit.
- Class 0 is the trap. A device that doesn't announce a class gets treated as Class 0 and the switch reserves 15.4 W, even if it only needs 3 W.
- PTZ cameras peak when they move, and heaters in outdoor cameras peak in winter. Budget for the worst moment.
- Leave headroom. Running a switch's PoE at its full budget leaves nothing for one more device, and some switches shut off ports by priority when they go over.
- Long cables and cheap cable lose more. Copper-clad aluminum cable runs hot under PoE. Use solid copper.