A PoE switch must supply every camera's peak draw, with IR on, plus headroom. Sixteen 4 MP eyeball cameras at 4.9 W each and one PTZ budgeted at 25.5 W draw about 104 W; with 25% headroom the switch needs a PoE budget of at least 130 W and one PoE+ (802.3at) port. This calculator does that sum for your own cameras and also shows the worst case, when the switch reserves power by class instead of by actual draw.
Last checked: 14 Oct 2026.
This page is the calculator. Why PoE budgets fail in Indian plants (DG changeover, surges, inrush after a power cut) is explained in Mama's guide to the PoE power budget for factory cameras in India.
How the calculator works
Inputs: number of fixed cameras and their peak draw with IR on, number of PTZ cameras and their peak draw, and headroom.
Peak draw (W) = fixed cameras × W each + PTZ × W each
PoE budget needed (W) = peak draw × (1 + headroom)
Port class = smallest PoE type whose power at the camera covers the camera's peak
Class reservation (W) = sum of the switch-side power of each camera's class
The PoE types, per the Ethernet Alliance overview of IEEE 802.3 (June 2018, checked 14 Oct 2026):
| Standard | Type | At the switch port (W) | At the camera (W) |
|---|---|---|---|
| IEEE 802.3af (PoE) | Type 1 | 15.4 | 12.95 |
| IEEE 802.3at (PoE+) | Type 2 | 30 | 25.5 |
| IEEE 802.3bt | Type 3 | 60 | 51 |
| IEEE 802.3bt | Type 4 | 90 | 71.3 |
The Ethernet Alliance slide rounds the 802.3af camera-side figure to 13 W; the 12.95 W figure comes from the IEEE 802.3af task force's "PSE and PD power limits" (22 May 2001): 37 V × 350 mA = 12.95 W, with 15.4 W the minimum at the switch.
Why the class reservation matters. Each camera announces a power class when it connects; per the same Ethernet Alliance overview, "Power Classification provides granular power levels to minimize wasted power". A switch may allocate by announced class rather than by measured draw, so a 4.9 W camera that announces Class 3 (or the default Class 0) uses 15.4 W of the switch's budget. The calculator's reservation figure assumes that worst case: every camera reserves the full power of its type (15.4, 30, 60 or 90 W). A camera that announces Class 1 or 2 reserves only 3.84 or 7 W at the switch, per the same overview. Check your switch's PoE allocation mode in its manual; if it allocates by class, size for the reservation figure.
Worked example: 8 to 32 cameras
Camera draw comes from one vendor datasheet: the Dahua DH-IPC-HDW4431V-SA, a 4 MP eyeball (turret) camera with 30 m IR, lists 2.7 W basic and 4.9 W maximum on PoE (802.3af), the maximum with H.265, analytics, WDR and IR intensity on (datasheet dated 30 Apr 2025, checked 14 Oct 2026). The table uses 2.7 W as a daytime figure and 4.9 W as the night-time peak; this mapping is an assumption. The PTZ is budgeted at 25.5 W, the most an 802.3at port guarantees at the camera. That is an assumption that fits a smaller PTZ; outdoor PTZs with long-range IR, wipers or heaters can need more than 25.5 W, and then an 802.3bt port or the camera's own power supply. Use your PTZ's datasheet figure.
| Cameras | IR off, 2.7 W each (W) | IR on, 4.9 W each (W) | IR on + 1 PTZ (W) | + 25% headroom (W) | Class reservation, worst case (W) | Switch to buy |
|---|---|---|---|---|---|---|
| 8 | 21.6 | 39.2 | 64.7 | 80.9 | 153.2 | 10-port, ≥ 81 W PoE, 1 × PoE+ |
| 16 | 43.2 | 78.4 | 103.9 | 129.9 | 276.4 | 18-port or 2 × 10-port, ≥ 130 W, 1 × PoE+ |
| 24 | 64.8 | 117.6 | 143.1 | 178.9 | 399.6 | 26-port, ≥ 179 W, 1 × PoE+ |
| 32 | 86.4 | 156.8 | 182.3 | 227.9 | 522.8 | 2 × 18-port or one 48-port, ≥ 228 W, 1 × PoE+ |
Port counts include one spare per switch for an uplink or a later camera; this is an assumption, not a rule. The "switch to buy" column assumes allocation by actual draw. If your switch allocates by class, the reservation column applies, and a 32-camera site needs more than 520 W of PoE budget.
Two things stand out. Night is the design case: this camera's maximum is 1.8 times its basic draw (4.9 W against 2.7 W). And the PTZ alone is about two-fifths of the draw at 8 cameras (25.5 of 64.7 W) and a quarter at 16.
The calculator's defaults use 7 W per fixed camera, an assumption for a bullet with stronger IR than the eyeball camera above; with 16 such cameras and one PTZ it gives 137.5 W peak and a 172 W budget.
What this number does not tell you
- Your camera's real draw. Datasheet maximums differ by model suffix and firmware. One datasheet is used here; confirm every model you buy.
- Cable loss on long runs. The camera-side figures already allow for a 100 m channel, but thin or copper-clad aluminium cable loses more, as the PoE explainer describes.
- Cold-start inrush. After a power cut every camera boots at once. A switch sized with no headroom can trip then.
- Whether the switch stays powered. A PoE budget means nothing if the switch is not on a UPS: the cameras go dark with it, as the PoE explainer shows.
- What the cameras can see. Power keeps a camera alive; it does not decide whether it watches the right machine. For camera and NVR detection issues, see NVR not detecting an IP camera.
Related guides
- PoE Power Budget for Factory Cameras in India: Sizing It Right
- NVR Not Detecting IP Camera: PoE Subnet, ONVIF and Activation Fixes by Brand
- NVR HDD Shows Uninitialized After a Power Cut
- Certified CCTV Finder
FAQ
How do I calculate the PoE budget for CCTV cameras? Add every camera's peak draw with IR and heater on, then add 20–30% headroom. Sixteen 4.9 W cameras and one PTZ at 25.5 W is 103.9 W; with 25% headroom the switch needs at least 130 W of PoE budget.
Is 802.3af enough for an IP camera? For most fixed domes, eyeballs and bullets, yes: 802.3af guarantees 12.95 W at the camera, and the 4 MP eyeball above peaks at 4.9 W. PTZ cameras and cameras with heaters usually need 802.3at (25.5 W) or 802.3bt.
Why does my switch run out of PoE power before the cameras add up? It may be reserving power by each camera's announced class, not by what the camera draws. Sixteen 802.3af cameras announcing Class 0 or 3 can reserve 16 × 15.4 = 246.4 W even if they draw under 80 W. Check the switch's allocation mode, or buy for the reservation figure.
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