PoE budget planning means adding up what every access point, camera and phone can draw, then checking that total against the switch's power budget, not just its port ratings. This guide shows how to size switch power for APs, cameras and phones, with a worked example you can adapt.
The short answer
- List each device's maximum draw and PoE class from its data sheet.
- Pick the planning figure per port: the class allocation the switch will reserve, not the average draw.
- Add up the ports on each switch to get the load in watts.
- Compare with the switch's PoE budget for the exact power-supply configuration you will buy.
- Add headroom and decide what must survive a power-supply failure.
- Confirm LLDP or CDP power negotiation so the switch allocates what devices actually request.
A port that is rated for 30 W does not mean the switch can give 30 W to every port at once. Per-port capability and total budget are separate numbers.
Per-port power: the IEEE classes
The Ethernet Alliance's Overview of IEEE 802.3bt gives the power a switch port (PSE) supplies for each class, and the power the powered device (PD) can use after cable losses:
| Class | Standard type | Power at switch port | Power at the device |
|---|---|---|---|
| 1 | 802.3af (Type 1) | 4 W | 3.84 W |
| 2 | 802.3af (Type 1) | 7 W | 6.49 W |
| 3 | 802.3af (Type 1) | 15.4 W | 13 W |
| 4 | 802.3at (Type 2) | 30 W | 25.5 W |
| 5 | 802.3bt (Type 3) | 45 W | 40 W |
| 6 | 802.3bt (Type 3) | 60 W | 51 W |
| 7 | 802.3bt (Type 4) | 75 W | 62 W |
| 8 | 802.3bt (Type 4) | 90 W | 71.3 W |
Class 5 and above need all four pairs of the cable. Vendors name the upper levels differently: Cisco's Catalyst 9300 data sheet calls 60 W models UPOE and 90 W models UPOE+.
Step-by-step method
1. Build the device list. For each device type, record the maximum power draw and PoE class from the manufacturer data sheet. Where a data sheet gives a power at the device, plan the port at the next class up, because the switch must also cover cable loss.
2. Choose a planning figure. The switch reserves power by class (or by what the device requests), so plan on the allocation, not on typical consumption. Use measured or typical draw only if you have confirmed the switch will allocate to match (see LLDP below).
3. Total per switch. Multiply ports by planning figure for each switch, because the budget belongs to the switch (or stack), not to the site.
4. Compare with the budget for your power-supply configuration. The same switch has several budgets. The Catalyst 9300 data sheet lists a PoE figure for each combination of primary and secondary supply; see the lookup below.
5. Add headroom. Choose your own growth allowance (extra APs, a camera or two) and keep the load below the budget by that margin.
6. Test the failure case. Work out what the switch can still deliver with one supply out.
Worked example
This example uses one data-sheet figure and labelled assumptions. The access point draw is from the Cisco Meraki CW9176I data sheet, which lists a 39 W maximum draw at 802.3bt for full function (with the USB port in use). Camera and phone figures are example assumptions; replace them with your own data sheets.
| Device | Qty | Source of figure | Planned power per port | Load |
|---|---|---|---|---|
| Wi-Fi 7 AP (CW9176I) | 20 | Data sheet: 39 W max draw; planned at Class 5 (45 W at port) | 45 W | 900 W |
| IP camera | 10 | Example assumption: Class 3 | 15.4 W | 154 W |
| IP phone | 30 | Example assumption: Class 2 | 7 W | 210 W |
The APs and cameras (30 ports, 1,054 W) go on one 48-port UPOE switch. The 30 phones (210 W) go on a 48-port PoE+ switch.
Switch 1: Catalyst C9300-48U. The data sheet's power table for this model lists these PoE budgets:
| Power supplies | PoE available | Against 1,054 W load |
|---|---|---|
| 1,100 W alone | 822 W | Short by 232 W |
| 1,100 W + 350 W | 1,172 W | 118 W spare, no failure cover |
| 1,100 W + 715 W | 1,537 W | 483 W spare; if the 715 W supply fails, the 1,100 W supply alone gives 822 W, so some PoE would be shed |
| 1,900 W alone | 1,622 W | 568 W spare; a second supply adds cover |
With the 1,100 W and 715 W pair, the budget passes but a single-supply failure does not. If the design must keep every AP up through a supply failure, the surviving supply must carry 1,054 W on its own; of the options above, only the 1,900 W supply does. That is the point of testing the failure case separately.
Switch 2: Catalyst C9300-48P. The default 715 W supply gives 437 W of PoE budget on its own per the data sheet, against a 210 W phone load, so it passes with room. If you had allocated phones at 15.4 W (462 W), the same supply would be short, which is why the planning figure matters.
Remember the AP side too: at 802.3at the CW9176I runs the 2.4 GHz radio at 2x2, disables USB and drops its uplink to 2.5G. Powering APs from PoE+ ports saves budget but costs function.
Per-port versus total budget
Cisco's data sheet notes that figures marked with an asterisk are limited by port count and port rating, for example 24 PoE+ ports at 30 W equal 720 W. Two switches with the same port rating can have very different budgets. Cisco's power-supply pairing tables show the point: 90 W on 21 ports of a 24-port UPOE+ switch needs a 1,100 W plus a 715 W supply, and a 48-port PoE+ switch at 30 W on all ports needs two 1,100 W supplies or a 1,100 W plus a 715 W supply.
Power-supply redundancy and headroom
The Catalyst 9300 data sheet states that the switch supports dual redundant power supplies, ships with one, and the second can be bought later; a single supply must sit in bay 1. For stacks, Cisco's StackPower guide describes two modes:
| StackPower mode | Behaviour |
|---|---|
| Sharing (default) | All supply power is pooled across the stack. If a supply fails and the remaining budget covers the load, nothing is affected; otherwise load is shed, PoE devices first |
| Redundant | The power from the largest supply is subtracted from the budget, so capacity is kept in reserve for a failure |
Cisco also states StackPower reserves 30 W for a switch that may be added to the stack. Other vendors use different mode names and rules, so read the data sheet for the model you are buying.
LLDP power negotiation
A switch first classifies the device electrically. The Ethernet Alliance overview explains that LLDP then lets the device fine-tune its demand, and the 802.3bt extensions cover 4-pair capability, autoclass and the maximum power the PSE has. Cisco's PoE configuration guide for the Catalyst 9300 covers CDP and LLDP negotiation, per-port power limits, port priority (low-priority ports are shut first in a shortage) and power policing. Use show power inline <interface> detail to see what was requested and allocated. Check that LLDP or CDP is enabled on the switch and supported by the device on the release you run.
Common mistakes
- Adding up port ratings instead of the switch's real budget.
- Reading the budget for a larger power-supply pair than the one in the quote.
- Planning APs at 802.3at when they need 802.3bt for full function.
- Ignoring that load shedding switches off ports in priority order.
- Expecting redundancy from two supplies whose surviving half cannot carry the load.
Frequently asked questions
How much PoE budget do I need for 20 access points?
Multiply the AP's planned port power by 20. For the example above, 20 APs at 45 W is 900 W before cameras and headroom. Take the AP's maximum draw from its data sheet.
Can a PoE+ switch power a Wi-Fi 7 access point?
Often yes, with reduced function. Check the AP data sheet: the CW9176I, for instance, reduces radios and disables USB at 802.3at.
What happens when the PoE budget is exceeded?
On Cisco's StackPower, load is shed with PoE devices first, in priority order (see the guide above). Check how your switch behaves and set priorities on critical ports.
Is the PoE budget the same with two power supplies?
No. Cisco lists a separate budget for each primary and secondary combination, and it is capped by port count.
What to include in your quote request
- Device counts by type and the PoE class or standard of each.
- The maximum draw from each data sheet.
- Switch model, port count and the PoE budget you need.
- Power-supply configuration and redundancy requirement.
- Stacking or StackPower plans.
- Growth allowance.
Send these with a quote request.
Related guides and products
See how to choose a campus switch and Wi-Fi 6, 6E or 7 access points, plus the Wi-Fi 7 readiness checklist. Switch examples: Cisco C9300X-24HX-A, Cisco C9350-48HX, Cisco C9300-24T-E, Meraki C9300-24P-M, Meraki C9300-48P-M. Access points: Cisco CW9176I, Arista AP-C460, Juniper AP47-WW.
Tools: run your own numbers in the PoE budget calculator, or download the PoE budget worksheet (Excel) to plan offline.