PoE Power Budget Calculator – Plan Your Switch Deployment
Power over Ethernet (PoE) simplifies network installations by delivering both data and electrical power over a single Cat 5e or Cat 6 cable. Whether you are deploying wireless access points, IP cameras, VoIP phones, or smart sensors, understanding your switch PoE power budget is critical before purchasing equipment. Running out of available power mid-deployment means some devices will fail to negotiate power — and that failure can be difficult to diagnose.
What Is a PoE Power Budget?
Every PoE-capable switch has two relevant power figures: the per-port maximum (e.g., 30 W for PoE+) and the total PoE budget— the maximum aggregate watts the switch's power supply can deliver across all active PoE ports simultaneously. A 24-port PoE+ switch with a 370 W budget can theoretically supply 30 W × 24 ports = 720 W, but the internal PSU is only rated for 370 W, because real-world deployments mix device types at varying loads. Always check the switch datasheet for the actual total budget figure.
PoE Standards at a Glance
IEEE has published three major PoE standards, each increasing the maximum power per port:
- IEEE 802.3af (PoE) — Up to
15.4 Wat the switch port (PD receives approximately 12.95 W after cable loss). Suitable for IP phones, basic cameras, and low-power IoT sensors. - IEEE 802.3at (PoE+) — Up to
30 W. Covers most enterprise wireless access points, mid-range PTZ cameras, and VoIP desk phones with large color displays. - IEEE 802.3bt Type 3 (PoE++) — Up to
60 W. Supports dual-radio Wi-Fi 6/6E APs, multi-sensor cameras, and smart LED lighting fixtures. - IEEE 802.3bt Type 4 (PoE++) — Up to
100 W. Enables thin clients, mini-PCs, monitors with USB-C charging, and high-powered outdoor cameras.
How to Use This Calculator
Enter your switch's total PoE budget in watts — you can choose from common presets or type the exact figure from your switch's datasheet. Then add each category of powered device (PD) by selecting a preset or typing a custom name, entering the power draw per port, and setting the quantity. The calculator instantly shows:
- Total watts consumed by all devices
- Remaining budget and headroom percentage
- A per-device breakdown with share of total consumption
- How many ports of each PoE standard your budget supports at full load
The 80% Headroom Rule
A widely followed best practice is to keep your PoE utilization below 80% of the switch's rated budget. This reserve accounts for three factors: devices briefly spike power during boot negotiation (a camera or AP can draw 20–30% above steady-state for a few seconds); power supply efficiency degrades with age; and future expansion almost always happens. Planning at 80% means you have a 20% buffer for real-world variation.
Cable Length and Power Loss
IEEE standards permit cable resistance to cause a measurable voltage drop, especially on longer runs. For PoE (802.3af), the standard allows up to 12.95 W at the PD end even though the switch port outputs 15.4 W. For PoE+, the switch can output up to 34.2 W to deliver 30 W at the device. When planning with older or thinner cable, add roughly 10–15% to each device's listed wattage to account for this loss.
Mixing Device Classes on One Switch
PoE negotiation uses the Link Layer Discovery Protocol (LLDP) or IEEE classification markers to request a specific power class. A PoE+ switch is backward compatible with lower-class devices: a 5 W IP phone draws only 5 W even though the port can supply 30 W. This means a mixed deployment of phones, cameras, and APs will always consume less total power than if every port were running at maximum — but you must still verify that the total does not exceed your budget at peak concurrency.
Practical Sizing Example
Suppose you are planning a floor deployment with 12 Wi-Fi 6 access points (25.5 W each), 8 IP cameras (5 W each), and 20 VoIP phones (6.3 W each). Total: (12 × 25.5) + (8 × 5) + (20 × 6.3) = 306 + 40 + 126 = 472 W. At 80% of budget, you need a switch with at least 590 W total PoE capacity — a standard 370 W switch would be insufficient and a 740 W model would be the right choice. Always round up to the next available model and verify the per-port wattage matches the highest power device in the list.