PoE Power Budget Calculator
Work out whether a Power-over-Ethernet switch has enough power budget to run a set of devices — IP cameras, wireless access points, VoIP phones or door controllers — before you plug them in. Enter the switch's total PoE budget, how many devices you want to power and their average draw, and the tool returns the total load, the remaining budget and the maximum number of devices the switch can support.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the switch's total PoE power budget in watts — this is the aggregate PoE figure from the datasheet, not the number of ports.
- Enter how many powered devices you plan to connect and their average power per device (15.4 W for 802.3af, 30 W for 802.3at/PoE+, up to 60–90 W for 802.3bt/PoE++).
- Read the total device draw, the remaining budget and the max supported device count, and check the verdict for whether the load fits.
How it works
Total device draw is simply the number of devices multiplied by the average power per device. The remaining budget is the switch's rated PoE budget minus that total; if it is negative the switch is over budget. The maximum number of devices is the switch budget divided by the per-device power, rounded down to a whole device. The tool measures power at the switch (the PSE side); the device actually receives a little less because of cable resistance and PoE class overhead.
Worked example
Worked example. A 24-port switch has a 370 W PoE budget and you want to power 20 access points that each draw about 15.4 W. Total draw = 20 × 15.4 = 308 W, leaving 370 − 308 = 62 W spare. The budget could support floor(370 ÷ 15.4) = 24 such devices, so 20 fits comfortably.
Common mistakes
- Confusing the number of PoE ports with the PoE power budget — a 24-port switch rarely has enough budget to run all 24 ports at full PoE+.
- Using the device's nameplate maximum instead of its typical average draw, which overstates the load; conversely, ignoring class overhead and cable loss understates it.
- Forgetting the per-port limit — a single 60 W device can be refused on an 802.3af port even when the overall budget has room.
Frequently asked questions
Does the switch deliver the full 15.4 W or 30 W to the device?
No. Those figures are measured at the switch (the power-sourcing equipment). After cable resistance the device receives roughly 12.95 W for 802.3af and 25.5 W for 802.3at, which is why standards quote two numbers.
What if the remaining budget is exactly zero?
It fits, but with no headroom. In practice leave a margin so brief power spikes, a warmer cabinet or an extra device don't push the switch over its budget.
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