- Total device (PD) load: 504 W across 56 devices.
- Switch (PSE) budget needed: 597 W — that's 93 W more than the PD load, which is worst-case cable loss (not waste). Always size a switch on PSE watts.
- With 20% headroom, provision at least a 746 W PoE budget (run below ~80% of the switch's rating).
- You need 2 switches (bound by both budget and ports) at 600 W / 48 ports each.
- Your fleet includes Type 2 (802.3at / PoE+) devices — every switch must support 802.3at on the ports serving them (and confirm the switch can deliver 802.3at on all those ports simultaneously, not just a few).
Size on the switch side, not the device side
Almost every free PoE calculator just adds up device wattages and stops. That under-sizes the switch, because power is sourced at the switch (PSE) and consumed at the device (PD), and the two differ by cable loss. A device rated 25.5 W at the far end draws about 30 W from the switch port. So this planner sums your devices, converts each to the PSE watts it truly consumes, adds design headroom, and only then recommends a switch — and it checks two independent ceilings: the total PoE budget in watts, and enough ports of the right 802.3af/at/bt type. A 48-port switch is not 48 × its per-port maximum; its real budget is set by the power supply.
Wi-Fi 7 changed the maths
Wi-Fi 7 (and high-power PTZ cameras with heaters) frequently need 802.3bt — a Wi-Fi 7 AP that boots on PoE+ often runs degraded, quietly dropping radios or spatial streams. Planning a refresh on last generation’s PoE+ budget is the fastest way to a network that “works” but underperforms. The tool flags any device whose full-function PoE type exceeds the switch you’re planning, and reminds you that 802.3bt high power needs all four cable pairs.
PoE standards & wattages (IEEE 802.3)
PSE = power at the switch port; PD = power the device receives. The gap is worst-case 100 m cable loss.
| Standard | Class | PSE (switch/port) | PD (device) | Pairs | Typical devices |
|---|---|---|---|---|---|
| Type 1 (802.3af) | Class 0–3 | 15.4 W | 12.95 W | 2-pair | Basic APs, fixed cameras, VoIP phones |
| Type 2 (802.3at / PoE+) | Class 4 | 30 W | 25.5 W | 2-pair | Wi-Fi 6 APs, PTZ cameras |
| Type 3 (802.3bt) | Class 5–6 | 60 W | 51 W | 4-pair | Wi-Fi 7 APs, PTZ + heater, multi-door controllers |
| Type 4 (802.3bt / Hi-PoE) | Class 7–8 | 90 W | 71.3 W | 4-pair | High-power APs, kiosks, PoE displays |
Type 4 is 90 W PSE / 71.3 W PD at the standard (the 95–100 W “PoE++” figures are marketing). Verified against: Ethernet Alliance · Sifos Technologies · Juniper · Cisco Catalyst 9000 · Ubiquiti · CablesAndKits.
PoE FAQs
How much PoE budget do I need?
Add up the power your devices draw (their PD rating), then size the switch on the higher PSE figure — because a switch delivers power at the port (PSE side) and the device receives slightly less (PD side) after cable loss. Then add ~20% headroom so you never run above about 80% of the switch’s PoE budget. This calculator does all three steps and shows the device load and the required switch budget side by side, so you can see the cable-loss gap explicitly rather than under-buying.
What is the difference between PSE and PD watts (and why does it matter)?
PSE (Power Sourcing Equipment) is the switch; PD (Powered Device) is the AP/camera/phone. IEEE guarantees a maximum at each end and the two differ by worst-case 100 m cable loss: 802.3af is 15.4 W PSE / 12.95 W PD; 802.3at (PoE+) is 30 W / 25.5 W; 802.3bt Type 3 is 60 W / 51 W; Type 4 is 90 W / 71.3 W. You size the switch’s PoE budget in PSE watts; the device only ever sees the PD figure. Budgeting against PD ratings under-sizes the switch — the single most common PoE planning mistake.
Does a Wi-Fi 7 access point need more than PoE+?
Usually yes. Many Wi-Fi 7 APs need 802.3bt (Type 3, ~30–40 W) for full performance — for example Juniper’s AP47 needs about 29 W and Class 6 (60 W PSE). On plain 802.3at (PoE+) they typically still power on but run degraded — dropping radios or spatial streams. So "it powered up on PoE+" does not mean the budget is right. The tool flags where a device’s full-function PoE type exceeds the switch you’re planning.
Why can’t a 48-port PoE switch power every port at maximum?
Because a switch’s total PoE budget is set by its power supply, and it is far lower than ports × per-port maximum. A 48-port 802.3bt switch is not 48 × 60 = 2,880 W — real budgets are more like 600 W. That is why you must size against the switch’s published total PoE budget, and why two ceilings matter: total watts AND the number of ports of the right PoE type. This planner enforces both and tells you which one is the binding constraint.
How much power do typical PoE devices use?
As rough, editable starting points: VoIP phones ~4–13 W; fixed IP cameras ~4–6 W; PTZ cameras ~12–25 W (heated/high-power domes 25–60 W, needing 802.3bt); Wi-Fi 5 APs ~7–13 W; Wi-Fi 6/6E APs ~12–25 W; Wi-Fi 7 APs ~25–40 W+ (802.3bt). These vary widely by model, so the calculator uses them only as defaults you should override with your own datasheets.
What about uplinks and cabling?
Uplinks (SFP/SFP+) carry data, not PoE, and are sized on throughput — a Wi-Fi 6/7 fleet easily oversubscribes a 1 Gbps uplink, so 10 Gbps+ uplinks are usually the right call. On cabling, 802.3bt Type 3/4 (high power) needs all four pairs terminated (Cat5e/Cat6); 802.3af/at use two pairs. The 100 m Ethernet limit still applies. The tool recommends an uplink tier and flags 4-pair requirements.
How accurate is this?
The IEEE 802.3af/at/bt PSE and PD wattages, the class-to-type mapping and the "size on PSE / two-ceiling" doctrine are taken from the Ethernet Alliance and IEEE references and cross-checked. The maths is deterministic and test-covered. Device wattages are indicative defaults you edit, and switch PoE budgets are the figure you target (they vary by model) — a Servnet specialist confirms the exact switch and budget before you buy.
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