Related tools
Need to size switch ports too? Use the PoE Switch Calculator. Need backup power? Estimate UPS runtime. Planning the rest of your IP camera system? Calculate network bandwidth or CCTV storage.
How a PoE Power Budget Is Calculated
Start with the device count multiplied by the maximum watts per device, then add planning headroom. The calculator compares that recommended required budget with the switch's available total PoE budget.
Base PoE load = devices x maximum watts per device
Headroom watts = base PoE load x headroom percentage / 100
Required PoE budget = base PoE load + headroom watts
Planning utilization = required PoE budget / available switch PoE budget x 100
Total PoE Budget vs Per-Port Power
Total PoE budget and per-port PoE capacity are different. A switch may have a 120 W total PoE budget, but individual ports may still be limited by their supported PoE standard. A high-power PTZ camera might require PoE+ or PoE++ even if the switch has plenty of total watts remaining.
PoE vs PoE+ vs PoE++
IEEE 802.3af / Type 1 supplies up to 15.4 W from the PSE, with up to 12.95 W available at the powered device. IEEE 802.3at / Type 2 supplies up to 30 W from the PSE, with up to 25.5 W at the device. IEEE 802.3bt / Type 3 supplies up to 60 W from the PSE, with about 51 W at the device. IEEE 802.3bt / Type 4 supplies up to 90 W from the PSE, with about 71 W at the device.
Vendor labels such as PoE++ are not always used identically, so IEEE standard and type names are the safer way to compare requirements.
Why PoE Power Is Lower at the Device
Some power is lost through cabling and delivery, so the maximum power available to the powered device can be lower than the maximum supplied by the PSE. The exact real-world loss depends on cable length, cable quality, current, and implementation.
How Much PoE Headroom Should I Leave?
Headroom is a planning choice rather than a fixed universal requirement. It can help account for startup conditions, IR illumination, heaters or blowers, PTZ movement, changing operating modes, future devices, and avoiding operation at the absolute power-budget limit.
PTZ and High-Power Cameras
PTZ motors, heaters, IR illuminators, white lights, speakers, or other integrated features may make some cameras require more PoE power. Use the actual manufacturer's maximum power specification instead of estimating from resolution or camera type alone.
Example PoE Budget Calculation
Eight cameras at 8 W each produce a 64 W base PoE load. A 20% planning headroom adds 12.8 W, so the recommended required budget is 76.8 W. Compared with a 120 W PoE switch budget, 43.2 W of planning margin remains.
FAQ
What is a PoE power budget?
A PoE power budget is the total amount of power a switch can provide to powered devices across its PoE ports. It is separate from the switch's AC input rating and separate from each port's maximum PoE capability.
How do I calculate the PoE budget for cameras?
Multiply the number of cameras or PoE devices by each device's maximum specified wattage, then add a planning headroom percentage. Use the manufacturer's maximum power specification when possible.
Is a 120 W PoE switch enough for 8 cameras?
It depends on the cameras' actual maximum power draw. Eight 8 W cameras have a 64 W base load, and with 20% headroom the planned requirement is 76.8 W, which fits within a 120 W PoE budget.
What is the difference between PoE and PoE+?
PoE commonly refers to IEEE 802.3af / Type 1, while PoE+ commonly refers to IEEE 802.3at / Type 2. PoE+ supports more power, but device compatibility still depends on supported standards, classes, cabling, and manufacturer requirements.
What is PoE++?
PoE++ is commonly used for higher-power IEEE 802.3bt devices, including Type 3 and Type 4. Vendors do not always use labels identically, so IEEE standard and type names are more precise.
Does every PoE port share the switch's total power budget?
Ports draw from the switch's total PoE budget, but each port also has its own supported PoE capability. A high-power device may need PoE+ or PoE++ even when the switch has total watts available.
Can a PoE+ switch power a standard PoE camera?
Usually, higher PoE standards can power compatible lower-power devices, but compatibility still depends on proper negotiation, switch implementation, cabling, and the camera manufacturer's requirements.
Why does a PoE camera use more power at night?
Some cameras may draw more power when IR illumination, white light, heaters, blowers, speakers, or PTZ movement are active. Not every camera behaves the same way, so check the maximum power specification.
How much spare PoE capacity should I leave?
There is no universal percentage. Headroom is a planning choice for startup conditions, changing operating modes, future devices, and avoiding operation at the absolute PoE budget limit.
Planning note
Power negotiation, supported classes, cabling, switch implementation, environmental features, and manufacturer requirements all matter. Treat the result as a planning estimate and verify device specifications before purchasing equipment.