Power
PoE power budget calculator
A switch has two capacities and people treat them as one: how many ports deliver power, and how much power it can deliver across all of them at once. This adds up the second. You supply the figures from your own documentation, because we do not publish wattages we cannot source to IEEE.
NO WATTAGES PUBLISHED
· YOUR FIGURES, OUR ARITHMETIC
· CSLB #976737 C-7 LOW VOLTAGE
· RUNS IN YOUR BROWSER
· COMMERCIAL ONLY
Budget calculator · Power
PoE power budget calculator
A switch has two capacities and people treat them as one: how many ports it has, and how much power it can deliver across all of them at once. This adds up the second. It publishes no wattage for any PoE standard — both sides come from your own documentation.
Your result will appear here.
Every assumption this tool makes
- It publishes no wattage for any PoE standard. IEEE does not publish the per-class figures on its free abstract pages and the standards themselves are paywalled, so every figure in circulation traces to vendor and reseller pages rather than to IEEE. A dropdown of classes carrying wattages would smuggle exactly those numbers into something that looks like a specification.
- Both sides of the sum are yours. The switch budget comes off the switch or its datasheet; each device draw comes off that device's datasheet. The tool does the arithmetic and nothing else.
- The headroom default of 20% is our operating practice, not a standard. No source establishes a required margin. It is editable and visible in the result.
- Cable losses are not modelled, and they vary with run length and conductor.
- A datasheet maximum is not a worst case. Devices draw more in cold conditions, and they do it at the same time.
Why there is no class dropdown
The obvious version of this tool would publish numbers we cannot source
Every other PoE calculator offers a dropdown of standards, each carrying a wattage. We deliberately do not.
Those figures are not on IEEE’s free pages, and the standards themselves sit behind a paywall. Which means every wattage in general circulation traces back to a vendor or reseller page instead of to the body that publishes the standard. This site does not print a number it cannot attribute, and a dropdown is not a loophole in that rule — it is the worst place to break it, because a dropdown looks like a specification.
It costs you nothing in practice. The number that decides your project is not the theoretical maximum of a class. It is what your actual switch can deliver across all its ports at once, with your actual devices connected, and both of those are printed in documentation you already have.
What IEEE does publish, and what we will therefore state:
IEEE 802.3bt-2018 is titled “IEEE Standard for Ethernet Amendment 2: Physical Layer and Management Parameters for Power over Ethernet over 4 pairs”, and its scope says “The maximum Powered Device (PD) power available is increased by this amendment to IEEE Std 802.3-2018 by utilizing all four pairs in the specified structured wiring plant.”
Source: IEEE Standards, standards.ieee.org/ieee/802.3bt/6749. Retrieved 4 September 2026.
So 802.3bt delivers power over all four pairs and raises the maximum available to the device, relative to the base standard. 802.3af and 802.3at are the earlier named amendments. That is the whole of what we assert.
Why it bites
Free ports and no free power look identical until they do not
A switch with spare ports can have no spare power. Nothing about it looks wrong: the ports are physically there, the cameras plug in, and the failure that follows does not announce itself as a power problem. It shows up as devices restarting under load, or as the highest-drawing camera dropping first, or as a system that is entirely stable until the first cold night when several devices ask for more at once and the budget runs out.
That last case is the one worth designing against, and it is why the headroom field exists. A datasheet maximum is not a worst case: devices that draw more in cold conditions all draw more simultaneously, which is precisely the moment a system sized with no margin fails. It passes every mild day and fails once.
The budget is also rarely all yours. Access control readers, intercom stations, wireless access points and phones frequently sit on the same PoE infrastructure, and the camera project is not the only claim on it. Add those as device rows too, or the answer is optimistic.
The longer treatment, including the moments where this reliably catches people out, is in the PoE power budget.
The other constraint
Power and data share the cable, so the cable's limits are the system's
A budget that adds up is not the whole answer, because the run itself has limits. TIA/EIA permits a 100 metre channel for copper, and that figure includes the patch cords at both ends, not only the cable in the wall. The practical permanent-link limit is therefore about 90 metres, and shorter again once pathway routing, vertical drops and slack are counted.
Cable choice interacts with power too, and the reason is heat rather than speed. Cat6a supports 10 Gigabit to the full 100 metre channel, and its construction handles the heat generated by higher-power loads in a bundle — which matters because cable in a commercial building sits packed in a tray with a lot of other cable, and a bundle carrying power warms up.
You can check a proposed run against those figures with the cable run length checker, and the discipline behind a cabling job is under structured cabling. Where readers and entry stations share the infrastructure, the same budget question covers them, which is why access control and camera work are usually surveyed together.
Two boundaries, as on every page here. We work on commercial premises only and not on private residences. And we do not hold a C-10 or a C-16, so we do not work on fire alarm systems; that is coordinated with your own licensed fire alarm contractor.