PoE Power Budget Calculator
Check whether a Power-over-Ethernet switch can drive your devices — power used, budget remaining and the maximum number of ports you can power.
How it works
Power used = devices × watts each · Remaining = budget − used · Max devices = ⌊budget ÷ watts each⌋
A PoE switch has a fixed power budget shared across all its ports, which is usually less than the sum of every port’s maximum. Each powered device (a PoE class) draws a set wattage, so you multiply devices by per-device draw and compare to the budget. Plan headroom: cable resistance means a device pulls a little more at the switch than it consumes, and running a switch at 100% budget leaves no room for surges.
Worked example
A switch with a 370 W budget powering 12 cameras at 15.4 W (802.3af Class 0) each uses 184.8 W, leaving 185.2 W — about 50% utilisation. At 15.4 W per port it could power up to ⌊370 ÷ 15.4⌋ = 24 devices.
Frequently asked questions
How many watts does each PoE standard deliver?
802.3af (PoE) provides up to 15.4 W at the switch (12.95 W at the device); 802.3at (PoE+) up to 30 W; 802.3bt (PoE++) up to 60 W (Type 3) or 90–100 W (Type 4). Use the switch-side figure for budgeting.
Why plan headroom instead of using the full budget?
Devices can briefly draw above their rated power at boot, and cable resistance adds loss. Keeping 10–20% of the budget free avoids the switch shedding power from ports when everything powers on at once.
Is the total port power the same as the PoE budget?
No. A switch may have 24 ports each capable of 30 W (720 W of capacity) but only a 370 W total budget. The budget, not the per-port maximum, limits how many devices you can run at full draw.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.