How to Calculate a PoE Power Budget (With Worked Examples)

Power over Ethernet (PoE) is one of the most convenient technologies in networking, and one of the most commonly mis-sized. A classic symptom is cameras that work perfectly during the day and reboot at night. When infrared LEDs switch on, power draw rises and the switch runs out of PoE budget.

This guide shows how to calculate a PoE budget properly, with worked examples for cameras, access points and phones.

Step 1: Know the PoE standards

The difference between switch-port power and device power is lost in the cable. Budget at the switch side.

Step 2: List every device at its maximum draw

Use the maximum consumption from each datasheet, not the typical figure. For cameras, this means IR on and heaters on where fitted. For access points, it means all radios active.

Step 3: Add headroom

Add 20–30% to the total. Headroom covers ageing, temperature, future devices and measurement differences.

Step 4: Check both limits

Check two limits:

• Per-port limit: each port must supply its device's maximum, for example 30 W for PoE+.
• Total budget: the switch's total PoE budget must exceed the sum of all devices plus headroom.

Worked example 1: 16 IP cameras

Sixteen 4 MP IR bullet cameras with a datasheet maximum of 8 W each:

• 16 × 8 W = 128 W
• +25% headroom = 160 W

A 16-port PoE+ switch with a total budget of at least 160 W is needed. Check the datasheet of models such as the GE1610-16P2SF.

Worked example 2: Office floor

• 6 Wi-Fi 6 access points at 15 W = 90 W
• 20 IP phones at 5 W = 100 W
• 4 dome cameras at 6 W = 24 W
• Total 214 W, +25% = about 270 W

A 24-port managed PoE+ switch with 10G uplinks and a budget above 270 W fits, for example the GE7722-P28X4-L3. Check the exact budget in the datasheet.

Worked example 3: Industrial cabinet

An outdoor cabinet with an industrial 8-port PoE switch, four cameras at 10 W and one access point at 20 W:

• PoE load: 60 W
• Switch's own consumption: around 10 W (check the datasheet)
• Total 70 W, +30% = 91 W, so choose a 120 W DIN-rail supply such as the DRP-120-48.

Common mistakes

1. Using "typical" instead of maximum power.
2. Forgetting IR, heaters and PTZ motors.
3. Ignoring the switch's own consumption when sizing external supplies.
4. Assuming every port can deliver full power at the same time.
5. Exceeding 100 m of cable without a long-range PoE switch. See our PoE solutions.

Need help?

Navijin engineers can size PoE budgets and power supplies for your project. Send your device list via our sales team.