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PoE Budget Calculator
Check whether your PoE switch can actually power the cameras and other devices you're planning to connect — or flip it around and work out how many devices a given switch budget can support. Enter your switch's PoE budget and add device rows to get an instant power and port check.
Mode
Your switch
Devices
Switch budget
Within budget
This checks total budget only — confirm the switch's per-port maximum separately, since a high total budget doesn't guarantee any single port can deliver a high-draw device.
How this calculator works
Start with your switch's total PoE budget and port count, then add one row per device group — a preset fills in a reasonable example wattage, which you can overwrite with the actual figure from your device's datasheet. The calculator adds up every device's load, applies your chosen headroom percentage, and checks the result against your switch's budget and port count as two separate limits. Switch to "How Many Cameras?" mode to run the same math backwards: given a switch budget and a device wattage, how many can it actually support.
PoE budget vs. device power
PoE numbers get confusing fast because two different power figures are in play at once. PSE power is what the switch (the Power Sourcing Equipment) is rated to deliver per port under its standard — 15.4W for 802.3af, 30W for 802.3at, 60W or 90W for 802.3bt. PD power is what the connected device (the Powered Device) actually receives after standard cable loss is accounted for, which is always somewhat lower. Neither of these is the same as your device's real rated draw, which comes from its own datasheet and is the number this calculator actually uses for the load estimate.
Why the switch wattage is not the whole story
A switch's headline PoE budget (say, 120W) is the total it can hand out across every port combined, not a guarantee about any single port. Two separate constraints have to both be satisfied: the total budget across all connected devices, and each port's own maximum capability, which this calculator can't verify since it depends on your specific switch model. A 16-port, 120W switch could comfortably power sixteen 5W readers, but the same switch might not be able to push a single 60W PTZ-with-heater out of one port even though the total budget has room — check your switch's datasheet for its per-port maximum before assigning a high-draw device to a single port.
Worked example
16-port PoE switch, 120W total budget, ten 4MP cameras at 8W each, 20% headroom.
| Step | Result |
|---|---|
| Total device load | 10 × 8W = 80W |
| Headroom allowance (20%) | 80W × 0.20 = 16W |
| Planning requirement | 80W + 16W = 96W |
| Remaining budget | 120W − 96W = 24W |
| Ports used / remaining | 10 used, 6 remaining |
This switch comfortably covers the ten cameras with headroom to spare on both power and ports. Add five more of the same camera (120W total load, 144W planning requirement) and the same switch would be over budget even though three ports are still free — the power budget runs out before the ports do.
PoE standards reference
| Type | IEEE standard | PSE power | PD power | Pairs used |
|---|---|---|---|---|
| Type 1 | 802.3af | 15.4 W | 12.95 W | 2 |
| Type 2 | 802.3at (PoE+) | 30 W | 25.5 W | 2 |
| Type 3 | 802.3bt | 60 W | 51 W | 4 |
| Type 4 | 802.3bt | 90 W | ≈71-73 W | 4 |
These are the standards' own reference ceilings, not a specific device's actual draw — a 4MP camera rated for 802.3af compatibility typically uses well under its 12.95W PD allowance in practice. Use the standard to confirm compatibility with your switch, and use the device's own datasheet for the wattage that actually drives this calculator's results.
Cable loss
Every meter of twisted-pair copper has resistance, and current flowing through that resistance turns some power into heat along the cable run rather than delivering it to the device — this is ordinary I²R power loss, the same physics behind voltage drop on any DC circuit. When the estimate is switched on, this calculator uses the worst-case channel resistance each PoE standard itself assumes: 20 Ω per 100m for 802.3af and 12.5 Ω per 100m for 802.3at, both of which reproduce the standard's own published gap between PSE and PD power exactly when combined with that standard's maximum current (for example, 0.35A² × 20Ω = 2.45W, matching the af PSE/PD difference of 15.4W − 12.95W). 802.3bt Type 3 and Type 4 both run two 2-pair feeds in parallel and share a documented worst-case channel resistance of 6.25 Ω per 100m — independently verified here the same way: 1.2A² × 6.25Ω = 9W (matching Type 3's 60W − 51W gap) and 1.73A² × 6.25Ω = 18.7W (matching Type 4's 90W − 71.3W gap). The calculator then estimates each device's current from its wattage at a nominal 52V PSE output to turn that resistance into a watts figure for your actual entered load, not the standard's theoretical maximum.
Common field mistakes
A few PoE sizing mistakes come up often enough to be worth calling out directly: planning purely from port count and ignoring the total wattage budget; reading a switch's headline power rating (often the switch's own consumption or a marketing figure) instead of its actual usable PoE budget; sizing PTZ cameras, heaters, and IR illuminators at their idle draw instead of their peak; treating a preset or datasheet "typical" wattage as a hard guarantee rather than a starting point; planning a job at exactly 100% of budget with no margin for growth or measurement variance; and assuming a switch's total PoE budget means any single port can deliver that much power, when the per-port maximum is usually lower and switch-specific.
Frequently asked questions
How much PoE power does an IP camera use?
It depends heavily on the camera. A basic 2MP fixed camera might draw 4-5W, while a PTZ with a heater can pull 30-40W or more. Always check the camera's own datasheet for its rated draw — the presets in this calculator are starting-point examples, not guarantees.
How many cameras can a PoE switch power?
That depends on your switch's total PoE budget, the actual wattage of each camera, and how much headroom you want to keep. Use the "How Many Cameras?" mode above to get a number based on both your power budget and your port count.
What is the difference between 802.3af and 802.3at?
802.3af (Type 1) delivers up to 15.4W from the switch (PSE) and about 12.95W at the device (PD) after standard cable loss. 802.3at (Type 2, often called PoE+) roughly doubles that to 30W PSE / 25.5W PD, enough for most PTZ cameras and access points.
What is 802.3bt?
802.3bt is the newer standard that adds Type 3 (60W PSE / 51W PD) and Type 4 (90W PSE / roughly 71-73W PD depending on the reference), using all four pairs in the cable instead of two. It's aimed at high-draw devices like PTZ cameras with heaters, video walls, and some access points.
Should I leave headroom on a PoE switch?
Most technicians plan with some margin rather than right at the switch's rated limit, since real-world draw can spike briefly during camera boot-up, IR turning on, or PTZ movement. This calculator defaults to 20% headroom as a planning convention, not an IEEE requirement — adjust it to match how your team normally specs jobs.
Does cable length reduce PoE power?
Yes. Every meter of copper adds resistance, and that resistance turns some of the power into heat along the way rather than at the device. The loss is usually small on a typical 30-50m run but grows with length, which is why this calculator offers an optional cable-loss estimate.
Is PoE switch wattage the same as camera power?
No, and mixing these up is one of the most common sizing mistakes. Switch wattage (PSE) is what the switch can source; the camera's actual draw (PD) is always somewhat lower once cable loss is accounted for. This calculator keeps the two separate rather than treating them as interchangeable.
Can I mix PoE and PoE+ cameras on one switch?
Yes. Most modern PoE switches negotiate power per port based on what each connected device requests, so af, at, and bt devices can share the same switch as long as the total draw stays within the switch's overall PoE budget.
Related CCTV tools
Once your power budget checks out, confirm the rest of the install: the IP Camera Bandwidth Calculator sizes your switch uplink, the NVR Storage Calculator or CCTV Storage Calculator works out drive space for the retention period you need, and the Battery Backup Calculator sizes backup power for the switch and NVR if the install needs it.