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PoE Switch Budget Calculator

Check a PoE switch power budget against the access points, cameras and phones you intend to connect to it.

About PoE Switch Budget Calculator

PoE budgets are quoted at the switch, but the device draws its class power at the far end of a cable that dissipates some of it. Adding a loss allowance before summing is what stops a switch that looks adequate on paper from shutting ports down. PoE switches drop ports silently when the budget is exceeded, and the devices that lose power are rarely the ones you would have chosen.

Formula

PoE Switch Budget

Required watts = devices × per-device draw × (1 + cable loss)

per-device draw
Class power of the powered device
cable loss
Resistive loss in the run, typically 5-15%

Worked example

With the default values below, PoE Switch Budget Calculator returns Total Power Required of 170.94. Change any input above and every figure here is recalculated in your browser.

Inputs used

Powered devicesminimum 0
12
Power draw per deviceminimum 0 W
12.95 W
Switch PoE power budgetminimum 1 W
240 W
Cable loss allowanceaccepts 0–100 %
10 %

Results

Total Power Required
170.94 W
Switch Budget Used
71.2%
Spare Budget
69.06 W
Maximum Devices This Switch Supports
16
Verdict
Comfortably within budget

Step by step

  1. 1Values used
  2. 2PoE Switch Budget
  3. 3Total Power Required= 170.94 W
  4. 4Switch Budget Used= 71.2
  5. 5Spare Budget= 69.06 W
  6. 6Maximum Devices This Switch Supports= 16
  7. 7Verdict= Comfortably within budget

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is PoE Switch Budget calculated?

Required watts = devices × per-device draw × (1 + cable loss) PoE budgets are quoted at the switch, but the device draws its class power at the far end of a cable that dissipates some of it. Adding a loss allowance before summing is what stops a switch that looks adequate on paper from shutting ports down.

Why does PoE Switch Budget matter?

PoE switches drop ports silently when the budget is exceeded, and the devices that lose power are rarely the ones you would have chosen.

What values do I need to enter?

This calculator takes 4 inputs: Powered devices, Power draw per device, Switch PoE power budget, Cable loss allowance. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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