PoE Budget Calculator
Total the PoE draw of your devices and check it against your switch — no black boxes.
Switch power budget
Devices
Result
- Total power draw
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- Remaining budget
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- 80% safe limit
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- Verdict
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- Required class (largest device)
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- More of the largest device
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How a PoE budget works
Power over Ethernet lets one cable carry both data and power, so an IP camera, a Dante speaker, an access point or a touch panel needs no local power supply. The switch (the PSE) pushes power to each device (the PD) up to a per-port ceiling defined by the IEEE class:802.3af 15.4 W, 802.3at 30 W, 802.3bt Type 360 W and Type 4 90 W. Those ceilings are the switch-side figure — after cable loss, a device actually receives a little less (an 802.3af port delivers up to 12.95 W at the device).
A switch also has one total budget for all ports together, not just a per-port limit. A 24-port PoE+ switch rarely has 24 × 30 W available — more often the whole switch is rated around 370 W. The budget calculation is simplytotal = Σ (quantity × watts), and you compare that total against the switch budget.
The calculator also applies the 80% safety rule: plan the switch at 80% of its rated budget (so the recommended maximum load is 0.8 × budget). That margin absorbs power-on spikes, voltage drop on long runs, temperature derating and the device you forgot. Finally, it checks the per-port class: the single largest device in your list sets the class every port must support, via the sameminPoeClassFor rule used across the toolkit.
Worked example
A 24-port PoE+ switch rated at 370 W powers 20 speakers at 12 W each and 4 PTZ cameras at 25 W each. Total draw is 20 × 12 + 4 × 25 = 340 W, leaving 30 W of raw headroom. But the 80% safe limit is only 0.8 × 370 = 296 W — so 340 Wdoes not fit and you should move some devices or choose a larger budget. The largest single device is 25 W, which requires an 802.3bt Type 3 port (a 25 W draw exceeds the 80% margin of an 802.3at port).
Frequently asked questions
What is a PoE power budget?
It is the total wattage a switch can deliver across all of its PoE ports at once. Add up the draw of every powered device and compare it to that budget — and keep the total at or below 80% of the rated figure for headroom.
What is the difference between 802.3af, 802.3at and 802.3bt?
They are the IEEE Power over Ethernet standards. 802.3af (PoE) delivers up to 15.4 W per port, 802.3at (PoE+) up to 30 W, 802.3bt Type 3 up to 60 W and Type 4 up to 90 W. A device must fit inside the class its port provides.
Why plan at 80% of the budget?
The 80% rule leaves headroom for power-on inrush spikes, voltage drop over long cables, temperature derating, and a few devices you did not count yet. Running a PoE switch at 100% of its budget is how installs fail on day one.
How do I find a device’s PoE class and draw?
Both are on the device datasheet. The class is the ceiling the switch reserves per port; the draw in watts is what the device actually uses in practice. This calculator uses the wattage for the total, then maps the largest device to its required class.
Does cable length matter?
Yes — long cables drop voltage, so the switch must deliver more than the device receives. The IEEE class ceilings already assume a worst-case 100 m cable. This version of the tool notes cable length but does not compute the drop yet.
Related calculators
- Switch Configurator — plan the whole switch (bandwidth, PoE and ports).
- IP Video Bitrate Calculator — size the streams those PoE cameras carry.
- Rack BTU / Cooling Calculator — the heat that PoE load puts into your rack.
Disclaimer: PoE budgets are planning estimates. Confirm the per-port class, total budget and any temperature derating with your switch manufacturer.