Free tool
PoE budget calculator.
Add the devices on the job and the switch's PoE budget. See if it powers them all, with room to spare, before you order the switch.
How a PoE budget works
A PoE switch shares one power budget across all its ports. Every camera, access point or phone takes a share. Add up what they need and see if it fits.
What the devices need + what the cable loses, with 20% spare, must fit the switch's budget
1.Set the switch
Its PoE budget in watts, its ports and their type. All three are on its datasheet.
2.Add the devices
Each one's watts and how many. Use the maximum from its datasheet.
3.Read the answer
Yes, tight or no, how much is spare, and what to change if it does not fit.
What each PoE type gives
| Type | Device gets, at most | Switch supplies per port |
|---|---|---|
| PoE (802.3af) | 12.95 W | 15.4 W |
| PoE+ (802.3at) | 25.5 W | 30 W |
| PoE++ Type 3 (802.3bt) | 51 W | 60 W |
| PoE++ Type 4 (802.3bt) | 71.3 W | 90 W |
What each class holds on the switch
| Class | Device draws up to | Switch reserves |
|---|---|---|
| Class 0 | 12.95 W | 15.4 W |
| Class 1 | 3.84 W | 4 W |
| Class 2 | 6.49 W | 7 W |
| Class 3 | 12.95 W | 15.4 W |
| Class 4 | 25.5 W | 30 W |
| Class 5 | 40 W | 45 W |
| Class 6 | 51 W | 60 W |
| Class 7 | 62 W | 75 W |
| Class 8 | 71.3 W | 90 W |
Worth knowing
Keep 20% spare
Heaters and IR lights draw more on a cold night, and devices get added later.
By draw or by class
Many managed switches hold each device's class allowance, often more than it draws.
Cable loses power
A longer run loses more on the way. PoE reaches 328 ft (100 m).
On a UPS
Plan the PoE plus about 30 W for the switch itself.
Not sure how the switch counts? Plan by class
A switch that reserves by class can run out with watts still unused. Planning by class never comes up short.
16 cameras at 7 W draw 112 W, and hold 246.4 W by class.
Where these figures come from
The PoE types and classes come from the standard itself and the industry group that explains it.
The PoE standard
PoE types 1 to 4 and classes 0 to 8
Up to 71.3 W at the device, 90 W from the switch
IEEE 802.3bt2018
Each class, at the device and at the switch
Class 3: 13 W and 15.4 W; Class 4: 25.5 W and 30 W
No standard sets these, so they are NexVolt's starting figures. Change them to your own:
Common questions
How much PoE budget do I need for 16 cameras?
Sixteen typical 7 W cameras draw 112 W. With the power each 150 ft cable loses on the way, the switch spends about 114.3 W. Keep 20% of the budget spare and look for at least 143 W of PoE budget: in the common sizes, a 195 W switch. Use the maximum watts from your camera's datasheet; cameras with IR or heaters draw more at night and in winter. If the switch budgets by class, those cameras hold 246.4 W, so look for at least 308 W.
What is the difference between PoE, PoE+ and PoE++?
Each is a version of the IEEE 802.3 standard that delivers more power per port. PoE (802.3af) gives the device up to 12.95 W, from 15.4 W at the switch. PoE+ (802.3at) gives up to 25.5 W, from 30 W. PoE++ (802.3bt) comes in Type 3, up to 51 W from 60 W, and Type 4, up to 71.3 W from 90 W. The difference between the two figures is what a full-length cable is allowed to lose.
Why does my switch run out of PoE before its budget?
Many managed switches budget by PoE class, not by what devices draw. A 7 W camera usually announces Class 3, and the switch holds 15.4 W for it whatever it really uses. Sixteen of those draw about 112 W but hold 246.4 W of the budget. Plan by class, or set the switch to budget by negotiated or measured power (LLDP, or a consumption or dynamic mode).
How far can PoE run?
328 ft (100 m) of Cat5e or Cat6, the Ethernet limit, including the patch cords at both ends. Past that, use a PoE extender, a switch closer to the devices, or fiber with a media converter and a local power supply.
Does the cable length change the PoE budget?
A little. A 20 W access point loses about 1.18 W on 150 ft of cable and about 2.58 W on the full 328 ft, so a long run costs the switch more than the device draws. The calculator adds each device's cable loss for the run length you enter, rather than assuming every cable is the full length.
What size UPS does a PoE switch need?
Add the PoE the switch spends to what the switch itself uses, usually around 30 W for a 24-port model. For the starting example on this page (18 devices, 180.6 W of PoE), that is about 211 W. Then pick a battery for how many minutes or hours the cameras must keep recording in an outage.
Can a PoE+ switch power a PTZ camera with a heater?
Usually not. A PTZ with a heater or blower can draw 60 W or more, and a PoE+ port gives a device at most 25.5 W. It needs a PoE++ Type 4 port (71.3 W at the device), a PoE++ injector, or its own power supply. The calculator says no when a device needs more than the switch's ports give, whatever the total budget.
Do Wi-Fi 7 access points need PoE++?
Often. Many draw about 30 W at full power, more than the 25.5 W a PoE+ port gives, so they need PoE++ ports or run with some radios turned down. Check the maximum on the datasheet. On a switch that budgets by class, a Wi-Fi 7 access point usually announces Class 5 and holds 45 W.
