PoE Budget Calculator

How to Use This Tool

This calculator is for anyone planning or expanding a PoE security camera system who needs to know whether a single switch or NVR can power every camera. You’ll need three things: how many cameras you’re running, roughly how many watts each one draws, and the total PoE budget of your switch or NVR — it’s printed on the unit or in its spec sheet (for example, 65 W or 130 W).

Enter your camera count, pick the power draw that matches your cameras, and type in your switch’s PoE budget. If you’re mixing camera types — say, mostly basic cameras plus one power-hungry PTZ — add the extra watts in the optional field. The result shows your total draw, the percentage of the budget used, and the headroom left. Aim to stay at or below 80% used; if you’re higher, you need a switch with a bigger budget or a second one to share the load.

When This Tool Is Most Useful

This calculator is most useful when you’re:

• Planning a new camera system and choosing a PoE switch or NVR that can power all of it
• Adding cameras to an existing switch and checking there’s enough power left
• Diagnosing cameras that reboot, drop offline, or won’t power on — a classic over-budget symptom
• Deciding between one larger switch or splitting cameras across two

Example Calculation

Picture a common setup: a homeowner wraps a two-story house in six 4MP PoE cameras (front, back, both sides, garage, and patio), adds a PoE video doorbell, and puts one IR-spotlight camera on the driveway for night coverage. Here’s the power math:

• Six standard 4MP cameras: 6 × ~7 W = 42 W
• One PoE doorbell: ~5 W
• One driveway camera with IR spotlight: ~13 W
• Total draw: ~60 W

To run this through the calculator above, you’d enter 6 cameras at about 7 W each and put 18 W in the “extra watts” field for the doorbell (~5 W) and the IR driveway camera (~13 W). They bought a budget 8-port PoE switch rated for a 65 W total budget — so that’s 60 W of 65 W, or about 92% used, well past the 80% safety line (roughly 52 W on this switch).

Why that’s a problem, even though 60 is less than 65. PoE draw isn’t steady. After a power blip, all eight devices try to reconnect at once, and cameras pull extra current at startup; at night the driveway camera’s IR and the doorbell spike further. Running at 92% leaves nothing for those surges, so the switch trips its protection circuit and a camera or two drop off — usually the last ones added. The fix is headroom: step up to an 8-port switch with a ~120–130 W budget, which puts the same cameras at about 50% used with room to add two or three more later. If replacing the switch isn’t an option, move the doorbell and driveway camera onto a second small PoE switch or injector to spread the load.

Common Mistakes

• Counting ports, not watts. A high port count means nothing if the wattage runs out first — an 8-port switch might only fully power four or five high-draw cameras.
• Ignoring the startup surge. Cameras draw extra current when they boot, so sizing to exactly 100% means a single reboot can trip the switch. Stay at or below 80%.
• Forgetting the power-hungry cameras. PTZ motors, heaters, and IR spotlights can draw three to five times a basic camera. Budget those individually rather than using one average.
• Confusing per-port max with total budget. A switch may deliver 30 W to any one port but only, say, 65 W across all ports combined. It’s the combined total that limits how many cameras you can run.
• Assuming an NVR’s built-in PoE is generous. Many NVRs with built-in PoE have a modest total budget. Check it before relying on it for spotlight or PTZ cameras.

Accuracy & Assumptions

This calculator uses typical power figures for each camera class. Actual draw varies by model, so check your cameras’ spec sheets when you can. Real numbers move with:

• Camera features — IR illuminators, spotlights, PTZ motors, and heaters all raise draw, sometimes only at night or in the cold
• PoE standard — 802.3af tops out near 15 W per port, 802.3at (PoE+) near 30 W, and 802.3bt (PoE++) higher; a port can’t exceed its standard
• Cable loss — long or thin runs lose some power as heat before it reaches the camera
• Startup surge — brief current spikes when cameras power on or reconnect after an outage
• Per-port vs total limits — both caps apply at the same time

Always size the switch with headroom to spare. Targeting about 80% of the budget covers surges and leaves room to grow.

Next Steps

Power is one half of a PoE run; distance is the other. If any camera sits far from the switch, check the PoE voltage drop over your cable length so it still gets enough power at the end. Not sure which PoE standard your gear needs? Compare 802.3af, at, and bt. Shopping for hardware? See the best PoE switches for security cameras. And if a camera is already dropping off, how far you can run a PoE camera covers the distance limits behind it.

Related Resources

Related calculators & charts

• PoE Voltage Drop Calculator — check the power reaching a camera at the end of a long cable run
• PoE Standards Comparison — 802.3af vs 802.3at vs 802.3bt power, voltage, and which cameras each suits
• NVR Storage Calculator — size the hard drive for the same camera system

Related guides

• Best PoE Switches for Security Cameras — the budget and features to look for
• How Far Can You Run a PoE Camera? — the 100 m data limit and how distance affects power

Browse all free security camera & NVR tools.

Frequently Asked Questions

How do I calculate my PoE power budget?

Add up the wattage each camera draws, then compare that total to the PoE budget printed on your switch or NVR spec sheet. Leave headroom by aiming to use no more than about 80% of the rated budget so the switch is not running at its limit. The calculator above does the math once you enter your cameras.

What happens if I exceed my switch PoE budget?

When demand exceeds the budget, the switch protects itself by cutting power to lower-priority ports or under-powering them. In practice that means some cameras will not power on, others reboot randomly, or the last cameras you added simply do not appear. The fix is a switch with a larger PoE budget or splitting cameras across two switches.

How many cameras can one PoE switch run?

It depends on the switch total PoE budget, not just its port count. An 8-port switch with a small budget might only fully power four or five cameras. Multiply your typical camera draw by the number of cameras and check it fits within the budget with headroom to spare, because a high port count is useless if the watts run out first.

How much power does a PoE security camera use?

A basic fixed IP camera draws about 4 to 7 W, one with IR or a spotlight around 10 to 13 W, and a PTZ or heated camera 20 to 30 W. Check each camera spec sheet, since features like night IR and motors raise the draw, sometimes only at night or in cold weather.

Do I need to leave headroom in my PoE budget?

Yes. Aim to use no more than about 80% of the rated budget. Cameras pull extra current at startup, and after a power blip they all reconnect at once, so a switch running near 100% can trip its protection circuit and drop cameras.

What is the difference between per-port and total PoE budget?

Per-port power is the most a single port can deliver, about 15 W on 802.3af, 30 W on 802.3at, and more on 802.3bt, while the total budget is what all ports share combined. Both limits apply at once, and it is usually the total budget that runs out first on a busy switch.

Can an NVR with built-in PoE power all my cameras?

Sometimes, but many NVRs with built-in PoE have a modest total budget, often enough for basic cameras but not several high-draw ones. Check the NVR PoE budget the same way you would check a switch, and add a separate PoE switch if you need more power.

Last updated: July 2, 2026