PoE Power Budget Calculator

Frequently Asked Questions

How much power does PoE deliver?

802.3af (Type 1) up to 15.4 W at the switch (~12.95 W at the device), 802.3at (PoE+) ~30 W, 802.3bt (PoE++) 60 W (Type 3) or 90 W (Type 4) at the port.

Why subtract cable loss?

Resistance in the twisted pair dissipates several watts over long runs, so the powered device gets less than the port budget - the calculator derates for cable length.

How do I know if my switch is over budget?

Sum every powered device's class draw and compare to the switch's total PoE budget (often less than ports × max). Exceeding it makes the switch deny power to lower-priority ports.

Can one switch power many cameras?

Only within its aggregate budget. A 24-port switch might support 24×15 W but only have a 370 W budget - plan to the budget, not the port count.

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Estimates for informational purposes only.

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This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

A PoE switch advertises a total power budget (watts) shared across all ports. Each powered device (PD) reserves power by its 802.3 class: 802.3af Type 1 reserves 15.4W at the port, 802.3at (PoE+) 30W, 802.3bt Type 3 up to 60W and Type 4 up to 90W. This tool multiplies each device count by its class reservation, applies a cable-length derating (longer Cat5e/6 runs lose power as heat in the copper, so the switch must reserve more), sums the draw, and subtracts it from the budget to show headroom or an over-budget warning.

Worked Example

A 370W switch powering 12 × 802.3af cameras (15.4W), 6 × 802.3at APs (30W), and 2 × 60W bt devices, on ~50m runs. Base draw = 12×15.4 + 6×30 + 2×60 = 184.8 + 180 + 120 = 484.8W - before derating already over a 370W budget. Even at 10m runs this configuration exceeds the switch; you would split devices across two switches or choose a higher-budget chassis. The tool surfaces this immediately with an over-budget flag.

Real-World Use

Installers size switches before deploying IP cameras, wireless APs, VoIP phones, door controllers, and LED lighting. The key question - "will this switch power every device on this floor with headroom?" - is answered directly, including how many more standard PoE+ devices can still be added. It also flags when a high-density 802.3bt deployment needs a switch with a larger or dual power supply.

Common Mistakes

Sizing to PD draw, not port reservation: the switch reserves the full class budget per port, not the device's typical use.

Ignoring cable loss: 90m+ runs of thin Cat5e drop several watts - reserve extra.

Forgetting the supply, not just the ports: a 48-port switch rarely powers all 48 at full 802.3at.

Mixing standards blindly: a Type 1 switch cannot deliver 802.3bt regardless of remaining budget.

Limitations & Related Tools

The cable derating here is a simplified linear approximation (~1% per 10m, capped ~20%); exact loss depends on conductor gauge, Cat5e vs Cat6/6A, ambient temperature, and 2-pair vs 4-pair delivery. Real switches also reserve per-port at negotiated, not always maximum, class. Confirm against the vendor's PoE budget table and LLDP power negotiation. Use the Subnet planner for the IP design and the Latency calculator for AP backhaul sizing.

PoE Power Budget Calculator

Frequently Asked Questions

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