PoE Power Budget Calculator

PoE Power Budget Calculator

PoE Power Budget Calculator

Add devices, get total PoE wattage and the right-sized switch class.

Device list

Each row: label, device class, quantity. The calculator sums wattage and adds switch overhead.

Results

Devices-
Sum of device draw-
With headroom-
Recommended switch-
Add devices to see a switch recommendation.

How this works

  • Each PoE class has a maximum draw at the powered device (PD). Switches budget by port and by total PoE pool (the "PoE budget" spec).
  • Real device draw is often 50-80% of the class max in steady state but the switch must reserve the full class allocation. Always size on class maximum.
  • Headroom protects against simultaneous startup spikes (cameras with IR LEDs powering on can briefly hit class max), PTZ heater loads in winter, and future expansion.
StandardClassPD max (W)Typical device
802.3af (PoE)Class 0-312.95Fixed indoor cameras, VoIP phones
802.3at (PoE+)Class 425.5PTZ, outdoor cameras with heaters
802.3bt Type 3 (PoE++)Class 5-651Multi-sensor cameras, access controllers
802.3bt Type 4 (PoE++)Class 7-871.3Pan-tilt cameras with wipers, LED panels
Switch PoE budgets are listed as total wattage across all ports (e.g., "24-port PoE+ with 380W budget"). A 24-port switch will not deliver 24 × 30W — it caps at the budget figure.

Worked example

Small office with 12 indoor fixed cameras (Class 3, ~13W each), 4 outdoor bullets with IR (Class 4, ~25W each), and 6 VoIP phones (Class 1, ~4W each):

  • Cameras: 12 × 13W = 156W
  • Outdoor bullets: 4 × 25W = 100W
  • Phones: 6 × 4W = 24W
  • Total: 280W. With 20% headroom: 336W.

Recommended: a 24-port PoE+ switch with at least a 370W PoE budget. Standard 380W models give you ~12% extra headroom over your margined figure — the working sweet spot.

Recommended IPSD products

PoE Switches
8 / 16 / 24 / 48-port PoE+ and PoE++ from NETGEAR, Cisco, Ubiquiti, Comnet
PoE Injectors & Midspans
Single-port and rack-mount midspans for retrofits
PoE Extenders
Push runs past the 100m UTP limit (Comnet, NVT Phybridge)
Cat6 / Cat6A Cable
Larger conductor gauge keeps voltage drop in spec on long PoE runs

FAQ

Does cable length affect PoE budget?

Yes. The 802.3 standards assume 100m of Cat5e/Cat6. Beyond that, voltage drop pushes the PD below the minimum input voltage. Use Cat6A or shorter runs for high-class devices. PoE extenders (Comnet, NVT Phybridge) extend usable range up to 600m+ over single-pair or coax.

Why is 20% headroom the recommendation?

Two reasons. First, devices draw above their nominal during cold-start (IR LEDs, heaters, motor warm-up). Second, real-world deployments grow. A switch sized exactly to current load is full at install — you cannot add even one more camera without forklift-replacing the switch.

What is the difference between PoE+ and PoE++?

PoE+ (802.3at) delivers up to 30W at the switch port (25.5W at the device). PoE++ (802.3bt) delivers up to 60W (Type 3) or 90W (Type 4) at the port. PoE++ uses all 4 pairs of the cable; PoE+ uses 2 pairs.

Can I use a smaller switch and stay under-budgeted?

Risky. You will trip per-port disable when the budget is exceeded — cameras drop offline, sometimes at the worst time. Size to class max + headroom. If budget is tight, use two smaller switches rather than one over-subscribed switch.

What about UPS sizing?

Your UPS must support the switch's total input (PoE budget + switch electronics, typically 1.1x PoE budget). For a 380W PoE budget, plan ~420W of UPS capacity. Add other equipment (NVR, monitors) on top.

Related guides

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