How this calculator works
Total draw is the sum of quantity × maximum watts for each device. Headroom is added on top, because switches behave badly when they run at their limit and devices draw more in winter or at night.
Required budget = Σ(qty × max W) × (1 + headroom %)
Each device is matched to the lowest PoE standard that can power it, and the calculator flags any device that needs more than the switch can deliver per port.
| Standard | Per port at switch | At device |
|---|---|---|
| 802.3af (PoE) | 15.4 W | 12.95 W |
| 802.3at (PoE+) | 30 W | 25.5 W |
| 802.3bt Type 3 | 60 W | 51 W |
| 802.3bt Type 4 | 90 W | 71.3 W |
Enter the device's maximum draw from its datasheet. The calculator compares it against the switch-side figures above, so leave some margin for cable loss on long runs.
Frequently asked questions
How much headroom should a PoE budget have?
20% is a common rule of thumb. Go higher when PTZs with heaters or outdoor cameras with IR are a large share of the load, since both peak at the same time on cold nights.
Why use maximum watts instead of typical?
A camera draws its maximum with IR on, heaters running or a PTZ moving. Planning on typical draw means the switch can start dropping ports exactly when the cameras matter most.
Do I need PoE+ for PTZ cameras?
Most mid-size PTZs need 802.3at (up to 25.5 W at the device). Large PTZs with heaters, wipers or long-range IR often need 802.3bt or a separate power supply. Check the datasheet.
What happens when a switch runs out of PoE budget?
Most managed switches stop powering the lowest-priority ports. Set port priority so entrance and critical cameras stay up, and split the load across two switches when the margin is thin.