Networking

PoE Power Budget Calculator

Check whether a switch has enough shared PoE power for your cameras, access points, or phones. Enter a device count, watts per device, optional safety margin, and the switch's available PoE budget. This calculator compares aggregate power; you must also check each port's supported power level and the devices' PoE compatibility.

Your PoE budget

Within budget

The entered load and margin fit the shared budget. Check per-port compatibility separately.

Total device power consumption: 48 W
Required power including margin: 57.6 W
Remaining PoE budget (after margin): 62.4 W
Budget utilization (including margin): 48 %

Status uses required power including margin: below 90% is Within budget; 90–100% is Near limit; above 100% is Over budget. Negative remaining watts mean a shortfall.

This checks shared capacity, not per-port compatibility. Cable losses, power negotiation, and device peaks are not automatically modeled.

Understanding and calculating a PoE power budget

A PoE power budget is the total power a switch can allocate to powered devices through its Ethernet ports. It is a shared allowance, not the maximum wattage of a single port. Use the manufacturer's PoE output budget for your installed power-supply configuration, rather than the switch's AC input rating or its own operating consumption.

Formula: total device power (W) = device count × watts per device. Required power (W) = total device power × (1 + safety margin ÷ 100). Remaining PoE budget (W) = switch budget − required power. Budget utilization (%) = required power ÷ switch budget × 100. Remaining budget and utilization both include the margin; a negative remaining value indicates a shortfall.

ToolVirox labels utilization below 90% as Within budget, from 90% through 100% as Near limit, and above 100% as Over budget. These are transparent planning thresholds, not a switch manufacturer's operating policy. Exact budget equality is Near limit because no planned headroom remains. Status uses unrounded values; displayed figures are rounded for readability.

The default 20% safety margin adds an allowance equal to one fifth of device consumption. It does not mean that 20% of the final switch capacity will be free. You can adjust the margin from 0 to 100%; an empty optional margin means 0%. A margin helps accommodate uncertainty and future changes, but no fixed percentage guarantees reliable operation.

Device consumption describes the load at the powered equipment. The switch supplies power at its ports, and cable losses can make the required supply higher. Switches may reserve power according to a negotiated allocation or power class instead of measured draw. Use maximum device specifications and consult the switch's allocation figures and cable-loss allowances before purchase; this calculator does not model those losses or negotiation automatically.

Account for operating features such as camera infrared illumination, heaters, or access-point radio modes when choosing device wattage. A quiet daytime reading can understate the peak load. The calculation assumes identical devices; for mixed equipment, use a correctly weighted per-device average of maximum requirements, or calculate group totals and add them before applying a margin.

Common mistakes include multiplying port count by the port's advertised maximum and treating that as the total budget, using average rather than peak demand, overlooking other powered devices, and double-counting capacity already allocated. If you enter a remaining budget from the switch interface, count only the additional devices you plan to connect. If you enter the full budget, include every device it must power.

A result within the aggregate budget is not a compatibility certificate. Check port count, per-port limits, supported PoE type and class, cable suitability, and the budget available under the intended power-supply or redundancy configuration. PoE watts also say nothing about network throughput or recording retention; use the related CCTV tools for those separate calculations.

Examples

4 devices with comfortable headroom

Input: 4 devices at 12 W each, 20% margin, 120 W switch PoE budget.
Result: 48 W device load; 57.6 W required; 62.4 W remaining; 48% utilization. Status: Within budget.

8 devices near the limit

Input: 8 devices at 12 W each, 20% margin, 120 W budget.
Result: 96 W device load; 115.2 W required; 4.8 W remaining; 96% utilization. Status: Near limit.

16 devices exceeding the planned budget

Input: 16 devices at 15 W each, 20% margin, 250 W budget.
Result: 240 W device load; 288 W required; −38 W remaining (38 W shortfall); 115.2% utilization. Status: Over budget. The device load alone fits, but the chosen margin does not.

24 devices sharing a larger switch

Input: 24 devices at 15 W each, 20% margin, 450 W budget.
Result: 360 W device load; 432 W required; 18 W remaining; 96% utilization. Status: Near limit. Per-port compatibility still needs checking.

Frequently asked questions

What is PoE power budget?

It is the shared power available for a switch to supply connected Ethernet devices. It is distinct from the switch's own consumption and from the maximum power of one port. The installed power supplies and configuration can affect the available total.

How much PoE power do I need?

Add the maximum demand of all devices you will connect, allow for cable losses and power allocation, and include an appropriate planning margin. For identical devices, multiply their count by the watts per device. Then check both the total switch budget and each port's capability.

What happens if I exceed a switch PoE budget?

Depending on the switch and its priority settings, additional power requests may be refused or lower-priority devices may lose power. Check the model's documentation. An Over budget result here compares demand including your margin; it does not necessarily mean the current measured load alone exceeds the physical budget.

Should I add a safety margin?

A margin is useful when requirements are uncertain or you expect changes. The calculator starts at 20%, but that is a planning choice rather than a PoE standard. Use peak specifications, account for cable losses and allocation rules, and choose a margin suited to your installation.

Is PoE+ or PoE++ relevant to power budget?

Yes. PoE+ commonly refers to IEEE 802.3at and PoE++ to higher-power IEEE 802.3bt equipment. Check the exact type, class, and power delivered at the device; a marketing label alone does not establish compatibility. A large total budget cannot compensate for a port that cannot supply a particular device.

Can all switch ports deliver maximum PoE power at the same time?

Only if the total available budget and the switch's other limits support that combination. Port count multiplied by a per-port maximum can exceed the advertised shared budget. Consult the specifications for your exact power-supply configuration instead of assuming every port can run at maximum together.

Last reviewed: September 22, 2026