PoE Budget Calculator

Switch PoE budget:

Enter the total watts the switch can deliver to powered devices across all PoE ports.

Slide 0-3000 W for common access-switch and chassis budgets; type an exact datasheet value above.

PoE ports available:

Count only ports that can provide PoE in this switch, stack, or injector shelf.

ports

Slide 0-192 powered ports for common switch stacks; type a larger count above if needed.

Planning reserve:

Keep this part of the switch budget unused before judging the plan healthy.

Slide the headroom policy from no reserve to a highly conservative 80% holdback.

Device watts basis:

Use actual PD watts for datasheets; use switch-side watts when copying values from a switch dashboard.

PD watts Switch-side Class ceiling

Cable loss allowance:

Adds switch-side watts above device-side draw when the basis is actual PD watts.

Slide extra loss for long, warm, bundled, or uncertain cable runs when using PD-side watts.

Device inventory:

Rows use device,count,watts,standard,priority,cable length m. Standards accept 802.3af, 802.3at, bt3, or bt4.

Keep one device type per row; quoted CSV names are supported.

Check the PoE inventory

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Boot surge allowance:

Optional extra draw for a restart scenario; leave 0 when planning reserve already covers it.

Slide only when modeling simultaneous restart, IR activation, or other temporary load spikes.

Minimum spare watts:

Set a fixed spare target for known future devices or site policy.

Rounding:

Choose how many decimals to show in visible tables and exports.

Metric	Value	Readout	Copy
{{ row.metric }}	{{ row.value }}	{{ row.readout }}

Device	Count	Standard	Priority	Switch W Each	Total Switch W	Ports	Status	Copy
{{ row.device }}	{{ row.count }}	{{ row.standard }}	{{ row.priority }}	{{ row.switchEach }}	{{ row.totalSwitch }}	{{ row.ports }}	{{ row.status }}

Priority	Ports	Switch W	Retained W	Action	Readout	Copy
{{ row.priority }}	{{ row.ports }}	{{ row.switchW }}	{{ row.retainedW }}	{{ row.action }}	{{ row.readout }}

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A Power over Ethernet plan can fail even when the data network looks correctly sized. A switch may have enough uplink capacity and enough Ethernet ports, then run out of PoE watts when access points start radios, cameras turn on infrared LEDs, or door controllers restart after a power event. Another design may have spare watts but too few PoE-capable ports for the endpoint count. Treating PoE as one simple watt total hides those separate constraints.

PoE budgeting starts with the relationship between power sourcing equipment and powered devices. The power sourcing equipment is usually a PoE switch, injector, or midspan. The powered devices are the endpoints that consume power through the cable, such as wireless access points, IP cameras, phones, badge readers, sensors, and small controllers. The published switch PoE budget is the aggregate DC power available to PoE ports, not the same thing as the switch's AC power-supply rating or its total chassis power draw.

PSE: Power sourcing equipment, such as a switch or injector that supplies PoE.
PD: Powered device, such as an access point, camera, phone, or controller that receives PoE.
Switch-side watts: The watts allocated or drawn at the switch before cable loss is removed.
PD watts: The watts expected at the endpoint after the cable run.

PoE budget diagram showing a PSE switch, cable loss, powered devices, reserve watts, fixed spare watts, and a separate port count check

The hard part is choosing the right watt basis. A datasheet usually describes what the endpoint needs as a powered device. A switch dashboard may show what the switch has allocated or measured at the port. IEEE class planning can reserve a published ceiling that is higher than normal running draw. All three can be valid, but they should not be mixed in the same inventory without a deliberate rule.

Reserve policy is a design choice rather than a standard value. Installers may hold back watts for night mode, startup loads, future endpoints, vendor firmware changes, or uncertainty in device datasheets. A tight design can work in a lab and still fail after a restart if several devices negotiate higher power at the same time.

Aggregate watts decide whether the switch or stack has enough total PoE capacity.
Powered ports decide whether every endpoint has a PoE-capable physical port.
Cable loss turns endpoint watts into a higher switch-side demand when the source numbers are PD watts.
Reserve leaves room for startup draw, night loads, firmware changes, measurement uncertainty, and future small additions.

How to Use This Tool:

Start with the switch capacity, then describe one device type per inventory row. Check watts and ports together before using the plan.

Enter Switch PoE budget from the switch, stack, or injector shelf specification. Use the PoE power budget, not the total AC power-supply rating.
Set PoE ports available to the count of ports that can actually provide PoE. A switch with extra non-PoE ports should not count those ports here.
Choose a Planning reserve. The Usable planning budget row subtracts that percent before judging the plan against the reserve policy.
Pick Device watts basis. Use PD watts for endpoint datasheet draw, Switch-side for values copied from a switch, and Class ceiling when the plan should reserve IEEE standard ceilings.
Set Cable loss allowance when using PD watts. Increase it for long, warm, bundled, or uncertain cable runs. The allowance is not applied when the entered values are already switch-side watts.
Enter Device inventory as CSV rows in the order device, count, watts, standard, priority, and cable length in meters. Standards such as 802.3af, 802.3at, bt3, and bt4 make ceiling warnings and class-ceiling planning more useful.
Use Advanced when you need a Boot surge allowance, a fixed Minimum spare watts target, or different display rounding. If Check the PoE inventory appears, fix the listed row before relying on the summary.

After the inputs look right, read Budget Ledger for the watt policy, Device Load Ledger for per-device warnings, Priority Shedding Plan for load triage, and PoE Load Stack for a visual budget handoff.

Interpreting Results:

Spare after targets is the main planning number. It subtracts the percent reserve, the fixed spare target, and planned switch-side draw. A negative value means the design is over the selected policy even when the raw switch budget seems large enough.

The watt status and port badge answer different questions. Healthy budget can still appear with a red port badge if the switch has enough watts but not enough PoE-capable ports. Check PoE port demand before treating the plan as ready for a bill of materials.

Needs input means the inventory has no usable rows or a row has a non-numeric count or watts value.
Over budget means Spare after targets is below 0 W.
Tight budget means spare before the fixed spare target is below 10% of usable budget, or the Boot surge check goes negative.
Device Load Ledger warnings are not cosmetic. Inferred standards, unknown standards, passive PoE, zero values, and ceiling warnings all deserve a datasheet or switch-port check.
A positive spare result is not a field certification. Verify per-port standards, vendor power modes, cable length, cable category, and endpoint negotiation before rollout.

Technical Details:

Power over Ethernet sends DC power over twisted-pair Ethernet cabling while the link still carries data. IEEE PoE classes define delivery limits at the power sourcing equipment and usable power at the powered device. The difference matters because cable resistance, pair count, temperature, and allocation policy can make switch-side demand higher than endpoint draw.

Budgeting reduces the installation to two linked capacity checks. The watt check compares planned switch-side draw with the switch budget after reserve and fixed spare targets. The port check compares powered endpoint count with available PoE ports. Priority affects the shedding guidance, but it does not reduce the baseline load.

Formula Core:

In PD watts mode, the cable-loss allowance raises each entered endpoint watt value before row totals are summed. In Switch-side mode, the entered watt value is already the switch-side value. In Class ceiling mode, known IEEE standards use their PSE ceiling for switch-side planning.

\begin{array}{lcl} W_{switch each} & = & W_{entered} \times (1 + \frac{L_{cable}}{100}) \\ W_{planned} & = & \sum (N_{count} \times W_{switch each}) \\ W_{usable} & = & W_{budget} - (W_{budget} \times \frac{R_{reserve}}{100}) \\ W_{policy spare} & = & max (0, W_{usable} - W_{fixed spare}) - W_{planned} \end{array}

PoE budget formula symbols and meanings
Symbol or value	Meaning	Where it appears
W entered	Watts entered for one device row	Device inventory watts column
L cable	Percent cable-loss allowance	Cable loss allowance
N count	Number of devices in the row	Device inventory count column
W usable	Budget remaining after percent reserve	Usable planning budget
W policy spare	Remaining watts after reserve, fixed spare target, and planned draw	Spare after targets

For example, 12 access points at 18 W each with a 10% cable-loss allowance consume 19.8 W per port at the switch. That row adds 237.6 W to Planned switch-side draw. If the switch budget is 740 W and reserve is 15%, the usable planning budget is 629 W before any fixed spare target.

PoE standard ceilings used for class-ceiling planning and row checks
Standard	Type	PSE ceiling	PD ceiling used	Pair note
802.3af	Type 1	15.4 W	12.95 W	2-pair PoE
802.3at	Type 2	30 W	25.5 W	2-pair PoE+
802.3bt Type 3	Type 3	60 W	51 W	4-pair capable
802.3bt Type 4	Type 4	90 W	71 W	4-pair PoE

Boot-surge planning adds a temporary percent increase to the planned draw and compares that restart draw with usable budget after the fixed spare target. The normal planned draw remains unchanged, so a design can fit steady-state demand while the Boot surge check warns that a simultaneous restart may exceed policy.

PoE status boundaries and corrective checks
Cue	Boundary	Corrective check
Needs input	No valid device rows, or count/watts cannot be read as numbers	Fix the row shown in Check the PoE inventory
Over budget	Spare after targets < 0 W	Reduce load, move devices, lower reserve policy only if justified, or use more PoE budget
Tight budget	Spare before fixed target < 10% of usable budget, or boot-surge spare < 0 W	Review high-draw rows, startup behavior, and reserve assumptions
Port shortage	PoE port demand > PoE ports available	Add PoE-capable ports even if watt spare remains positive
Row warning	Unknown standard, inferred standard, passive PoE, zero value, or class ceiling mismatch	Check datasheets and switch power settings before procurement

Accuracy Notes:

A PoE budget is an engineering estimate, not proof that every endpoint will negotiate and power up in the field. The arithmetic is deterministic, but the source numbers can be wrong or incomplete.

Cable-loss allowance is a planning percent, not a full thermal or conductor-resistance model.
Class-ceiling planning is intentionally conservative when measured draw is much lower than the IEEE ceiling.
Passive PoE, vendor-specific high-power modes, and per-port caps require manual compatibility checks.
The inventory is calculated in the browser without a server lookup. Treat device names and exports as sensitive if they identify real sites or equipment, and avoid sharing a filled-in URL unless that is intended.

Worked Examples:

Access switch with enough watts but too few ports

A 740 W switch with 48 PoE ports, 15% reserve, 10% cable loss, and the sample device inventory produces about 583.0 W of Planned switch-side draw. The plan still has about 46.0 W of Spare after targets, but PoE port demand is 54 ports. The port badge shows 6 ports short, so the device group needs another PoE-capable switch or fewer endpoints on that switch.

Class-ceiling audit for the same endpoint list

Switching Device watts basis to Class ceiling reserves the PSE ceiling for every recognized standard. The same sample rows rise to about 1,036.0 W of Planned switch-side draw, and Spare after targets becomes about 407.0 W short. That result is conservative, but it shows what happens when the switch is expected to hold class maximums instead of normal draw.

Restart scenario with steady-state spare

If the steady-state sample keeps its 46.0 W spare but Boot surge allowance is set to 20%, the Boot surge check rises to about 699.6 W. With the same 15% reserve, surge spare goes negative by about 70.6 W, so the status becomes Tight budget even though ordinary planned draw still fits.

Inventory row with bad watt text

A row such as Lobby AP,2,about 18,802.3at,high,50 triggers Check the PoE inventory because watts must be numeric. Replace about 18 with 18, then check Device Load Ledger for ceiling or standard warnings.

FAQ:

Should I use PD watts, switch-side watts, or class ceiling?

Use PD watts for endpoint datasheet draw and add a cable-loss allowance. Use Switch-side for values copied from switch reporting. Use Class ceiling when procurement or policy should reserve IEEE maximums.

Why can the watt budget pass while the port badge fails?

Watts and physical PoE ports are checked separately. A switch can have enough aggregate power for the planned draw and still lack enough PoE-capable ports for the endpoint count.

Why did a row infer an IEEE standard?

When the standard cell is blank, the entered PD watt value is compared with common IEEE PD ceilings. The inferred standard is a warning cue, not a substitute for checking the device datasheet.

What should I do with a passive PoE warning?

Treat it as a manual compatibility stop. Passive PoE may not negotiate like IEEE PoE, so confirm voltage, polarity, injector behavior, and device support before connecting equipment.

Why does the inventory check say watts must be a number?

The watts cell must contain a numeric value such as 18 or 18.5. Remove words, ranges, and notes from that cell, then use Device Load Ledger to review the parsed row.

Is my device inventory sent to a server?

The budget math runs in the browser without a server lookup. Be careful with copied tables, downloaded files, and shared URLs if the inventory includes real device names or site details.

Glossary:

PSE: Power sourcing equipment, usually the PoE switch, injector, or midspan that supplies power.
PD: Powered device, the endpoint that receives PoE through the Ethernet cable.
Switch-side watts: Power budgeted or measured at the switch before cable loss is removed.
PD watts: Power expected at the endpoint after the cable run.
Class ceiling: The IEEE standard maximum reserved for a known PoE class or type.
Planning reserve: A percent of switch budget intentionally held back before judging spare capacity.
Boot surge: A temporary restart or activation load above steady-state draw.
Passive PoE: Power delivery that may not use normal IEEE negotiation and needs a manual compatibility check.

References:

IEEE 802.3bt-2018 standard page, IEEE SA.
Overview of 802.3bt Power over Ethernet Standard, Ethernet Alliance.
What Is Power over Ethernet?, Cisco.
User guide for Power Over Ethernet cabling system, Legrand, 2023.