PoE Budget Calculator

A PoE switch has a total power budget shared by all its ports, and it is usually smaller than ports x max per port. A 24-port switch with a 370 W budget can't give every port 30 W.

The calculator takes your budget, keeps back the headroom you choose, and divides what's left by the draw of one device. The answer is capped at the number of PoE ports.

For device draw, use the power the switch allocates at its end of the cable. The PoE standard classes, measured at the switch:

Swipe the table sideways to see all columns ->

The default is a switch with a 370 W budget, 24 PoE ports, 20% headroom, and devices drawing 18 W each:

• Usable budget: 370 x 0.8 = 296 W
• Devices: 296 / 18 = 16.4, so 16 devices
• Power used: 16 x 18 = 288 W, leaving 8 W

So only 16 of the 24 ports can power these devices. Plan the other 8 for non-PoE gear, or pick a switch with a bigger budget.

Many switches reserve power by PoE class, not by what the device actually uses. A class 4 device may reserve the full 30 W even if it draws 12 W. Check whether your switch can allocate by actual draw (often called LLDP or dynamic allocation).

20% is a common rule. It covers startup surges, devices that draw more with heaters or IR lights on, and one or two devices added later.

Use the maximum power in the device's datasheet, not the typical figure. Wi-Fi 6 and 6E access points often need PoE+ or more, and cameras with heaters can double their draw in winter.