Sizing tool
PoE Power Budget Calculator
Quick answer
Divide the total device draw by 0.8, then buy a switch whose published budget is larger than that number.The 20% is the reserve for IR at night, motor start-up and ageing. Port count has to cover the device count as well — a big budget on too few ports is a different mistake from too many ports on a small budget.
The budget printed on a PoE switch is the output of its power supply, shared across every powered port. It is not a per-port allowance, and it does not grow when ports are left empty. That single fact explains most of the sizing errors on camera sites: a 24-port 400 W switch with twenty-four 25 W PTZ heads needs 600 W and will not deliver it, even though each individual port is well within what one port can supply.
This page does the arithmetic in both directions. Enter the devices you have and it returns the total load, the budget you need with the reserve kept, and the models in the range that cover it — including the ones that fit on budget but not on ports.
Enter your devices
Use the watts on the device label or in its datasheet. Where a device lists a range, use the higher figure — that is the one that happens at night.
Result
Enter a device count to see which models cover the load.
Not financial advice on your camera list — send the actual labels and we will size it with you.
The formula, and why each term is there
Σ device watts is the sum of the labels at peak, not the average. A camera that draws 4 W in daylight and 7 W with IR on counts as 7 W. A PTZ that draws 30 W while panning counts as 30 W.
÷ 0.8 keeps a fifth of the supply in hand. Three things consume it: start-up surge when motors and IR drivers switch on, the extra draw on a cold night, and the fact that a power supply delivers less than its rated output as it ages and as cabinet temperature rises.
Then check ports. Powered ports must be at least the device count. If the budget needs 300 W and the device count is 22, you need a 24-port model — a 16-port unit with the same budget cannot take the load because it has nowhere to plug it in.
The reverse check matters too: a 4-port unit with a 65 W budget covers four domes and nothing else. Devices that need more than the switch can pay for are usually covered with aPoE injector on a separate supply, which keeps them off the switch budget entirely.
Three worked examples
Calculated against the published budgets in this range, with the 20% reserve kept and the port count applied. Every figure below is produced from the same data as the model pages.
| Site | Devices | Load | Budget needed | Models that fit |
|---|---|---|---|---|
| 8 fixed domes | 8 | 48 W | 60 W | HX-0802PE (8p / 120 W), HX-0803PE (8p / 120 W), HX-0803PEG (8p / 120 W) +12 more |
| 16 domes + 4 PTZ | 20 | 196 W | 245 W | HX-X2403PE (24p / 300 W), HX-X2403PEG (24p / 300 W), HX-2404PE (24p / 400 W) +1 more |
| 12 APs + 6 domes | 18 | 132 W | 165 W | HX-X2403PE (24p / 300 W), HX-X2403PEG (24p / 300 W), HX-2404PE (24p / 400 W) +1 more |
Every model, by budget and port count
This is the raw material the calculator uses. Budgets are pooled; the "cameras at 6 W" column is floor(budget × 0.8 ÷ 6) capped at the port count.
| Model | Powered ports | Budget | W per port (even load) | Domes at 6 W | PTZ at 25 W |
|---|---|---|---|---|---|
| HX-0402PE4+2-Port 100M PoE Switch | 4 | 65 W | 16.3 W | 4 | 2 |
| HX-0403PEG4+2+1-Port Gigabit PoE Switch | 4 | 65 W | 16.3 W | 4 | 2 |
| HX-M0402PEAll-in-One 4+2-Port 100M PoE Switch | 4 | 65 W | 16.3 W | 4 | 2 |
| HX-X0402PE4+2-Port 100M PoE Switch | 4 | 65 W | 16.3 W | 4 | 2 |
| HX-X0402PEG4+1+1-Port Gigabit PoE Switch | 4 | 65 W | 16.3 W | 4 | 2 |
| HX-0802PE8+2-Port 100M PoE Switch | 8 | 120 W | 15.0 W | 8 | 3 |
| HX-0803PE8+2+1-Port 100M PoE Switch | 8 | 120 W | 15.0 W | 8 | 3 |
| HX-0803PEG8+2+1-Port Gigabit PoE Switch | 8 | 120 W | 15.0 W | 8 | 3 |
| HX-D0802PE8+2-Port 100M PoE Switch | 8 | 120 W | 15.0 W | 8 | 3 |
| HX-X0802PE8+2-Port 100M PoE Switch | 8 | 120 W | 15.0 W | 8 | 3 |
| HX-X0802PG8+2-Port 100M PoE Switch | 8 | 120 W | 15.0 W | 8 | 3 |
| HX-X0803PEG8+2+1-Port Gigabit PoE Switch | 8 | 120 W | 15.0 W | 8 | 3 |
| HX-X1603PE16+2+1-Port 100M PoE Switch | 16 | 200 W | 12.5 W | 16 | 6 |
| HX-X1603PEG16+2+1-Port Gigabit PoE Switch | 16 | 200 W | 12.5 W | 16 | 6 |
| HX-1603PE16+2+1-Port 100M PoE Switch | 16 | 330 W | 20.6 W | 16 | 10 |
| HX-1603PEG16+2+1-Port Gigabit PoE Switch | 16 | 330 W | 20.6 W | 16 | 10 |
| HX-X2403PE24+2+1-Port 100M PoE Switch | 24 | 300 W | 12.5 W | 24 | 9 |
| HX-X2403PEG24+2+1-Port Gigabit PoE Switch | 24 | 300 W | 12.5 W | 24 | 9 |
| HX-2404PE24+2+2-Port 100M PoE Switch | 24 | 400 W | 16.7 W | 24 | 12 |
| HX-2404PEG24+2+2-Port Gigabit PoE Switch | 24 | 400 W | 16.7 W | 24 | 12 |
Frequently asked
How do I calculate the PoE power budget I need?
Add up the watts printed on every device label at its peak draw, add 20% for start-up surge, IR load and ageing, and choose a switch whose published budget exceeds that total. Port count must also be at least the number of powered devices.
Is the PoE budget per port or shared?
Shared. The budget is the output of the power supply, pooled across all powered ports. A 400 W switch with 24 ports averages 16.6 W per port if every port is loaded, but one port may draw 30 W while another draws 6 W, as long as the total stays inside the budget.
Why keep a 20% reserve?
Because the label is not the peak. IR illuminators and heaters switch on at night, motors draw surge current at start-up, and power supplies lose output capacity as they age and as cabinet temperature rises. A switch sized to 100% of the label sum has no allowance for any of that.
How many cameras can a 400 W PoE switch power?
About 53 fixed domes at 6 W on paper, but the port count caps it: a 24-port 400 W switch powers 24 domes (144 W) comfortably, or about 12 PTZ heads at 25 W. The budget decides whether the ports can all be used at the draw you have.
Does cable length reduce the power available?
Yes, through voltage drop. Over 100 m of Cat5e at a 30 W load the drop is small but real, and a device at the far end of a long thin run sees less voltage than one next to the switch. Use Cat5e or better, keep runs inside the 100 m channel limit, and prefer 2-pair mode A wiring as specified on each model.
What happens if the total draw exceeds the budget?
The switch refuses power to the last devices in its start-up order, or drops devices under load. On a camera site this appears at dusk when IR and heaters come on: cameras that ran all afternoon reboot in a loop.
Have the device list and the port count?
Send both and we will return the model, the budget margin and the lead time.
Related: the 8-port,16-port and24-port ranges, and thePoE switch for IP cameras page.